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Sample records for 15n spin relaxation

  1. Water proton spin saturation affects measured protein backbone 15 N spin relaxation rates

    NASA Astrophysics Data System (ADS)

    Chen, Kang; Tjandra, Nico

    2011-12-01

    Protein backbone 15N NMR spin relaxation rates are useful in characterizing the protein dynamics and structures. To observe the protein nuclear-spin resonances a pulse sequence has to include a water suppression scheme. There are two commonly employed methods, saturating or dephasing the water spins with pulse field gradients and keeping them unperturbed with flip-back pulses. Here different water suppression methods were incorporated into pulse sequences to measure 15N longitudinal T1 and transversal rotating-frame T1ρ spin relaxation. Unexpectedly the 15N T1 relaxation time constants varied significantly with the choice of water suppression method. For a 25-kDa Escherichiacoli. glutamine binding protein (GlnBP) the T1 values acquired with the pulse sequence containing a water dephasing gradient are on average 20% longer than the ones obtained using a pulse sequence containing the water flip-back pulse. In contrast the two T1ρ data sets are correlated without an apparent offset. The average T1 difference was reduced to 12% when the experimental recycle delay was doubled, while the average T1 values from the flip-back measurements were nearly unchanged. Analysis of spectral signal to noise ratios ( s/ n) showed the apparent slower 15N relaxation obtained with the water dephasing experiment originated from the differences in 1H N recovery for each relaxation time point. This in turn offset signal reduction from 15N relaxation decay. The artifact becomes noticeable when the measured 15N relaxation time constant is comparable to recycle delay, e.g., the 15N T1 of medium to large proteins. The 15N relaxation rates measured with either water suppression schemes yield reasonable fits to the structure. However, data from the saturated scheme results in significantly lower Model-Free order parameters (< S2> = 0.81) than the non-saturated ones (< S2> = 0.88), indicating such order parameters may be previously underestimated.

  2. Mapping membrane protein backbone dynamics: a comparison of site-directed spin labeling with NMR 15N-relaxation measurements.

    PubMed

    Lo, Ryan H; Kroncke, Brett M; Solomon, Tsega L; Columbus, Linda

    2014-10-01

    The ability to detect nanosecond backbone dynamics with site-directed spin labeling (SDSL) in soluble proteins has been well established. However, for membrane proteins, the nitroxide appears to have more interactions with the protein surface, potentially hindering the sensitivity to backbone motions. To determine whether membrane protein backbone dynamics could be mapped with SDSL, a nitroxide was introduced at 55 independent sites in a model polytopic membrane protein, TM0026. Electron paramagnetic resonance spectral parameters were compared with NMR (15)N-relaxation data. Sequential scans revealed backbone dynamics with the same trends observed for the R1 relaxation rate, suggesting that nitroxide dynamics remain coupled to the backbone on membrane proteins.

  3. Direct measurements of protein backbone 15N spin relaxation rates from peak line-width using a fully-relaxed Accordion 3D HNCO experiment.

    PubMed

    Chen, Kang; Tjandra, Nico

    2009-03-01

    Protein backbone (15)N spin relaxation rates measured by solution NMR provide useful dynamic information with a site-specific resolution. The conventional method is to record a series of 2D (1)H-(15)N HSQC spectra with varied relaxation delays, and derive relaxation rate from the following curve fitting on the resonance intensities. Proteins with poorly resolved spectra often require several 3D HNCO spectra to be collected on a (15)N/(13)C double labeled protein sample. In order to reduce the relaxation dimension Carr et al. (P.A. Carr, D.A. Fearing, A.G. Palmer, 3D accordion spectroscopy for measuring N-15 and (CO)-Carbon-13 relaxation rates in poorly resolved NMR spectra, J. Magn. Reson. 132 (1998) 25-33) employed an Accordion type HNCO pulse sequence to obtain (15)N or (13)C T(1) relaxation rates by numerical fitting of the relaxation interfered free induction decay (FID) data. To avoid intensive analysis of the time domain data, we propose a modified protocol to measure (15)N T(1) and T(2) relaxation rates from easily obtained line-widths in an Accordion HNCO spectrum. Both T(1) and T(2) relaxation could be simultaneously convoluted into the constant-time evolution periods of (13)C' and (15)N, respectively. The relaxation delay was allowed to reach at least 3 x T(1) or 3 x T(2) so that the signal was substantially decayed by the end of the FID, and the resulting peak full-width at half height (FWHH) could be directly used to calculate relaxation rate. When applied to the 76-residue Ubiquitin and the 226-residue glutamine-binding protein (GlnBP), this method yielded T(1) and T(2) values deviating on average by 4-6% and 5-7%, respectively, from the measurements based on the conventional 2D method. In comparison, the conventional methods possessed intrinsic error ranges of 2-4% for T(1) and 3-6% for T(2). In addition to comparable accuracy, the fully-relaxed Accordion HNCO method presented here allowed measurements of relaxation rates for resonances unresolved in

  4. Backbone dynamics of barstar: a (15)N NMR relaxation study.

    PubMed

    Sahu, S C; Bhuyan, A K; Majumdar, A; Udgaonkar, J B

    2000-12-01

    Backbone dynamics of uniformly (15)N-labeled barstar have been studied at 32 degrees C, pH 6.7, by using (15)N relaxation data obtained from proton-detected 2D (1)H-(15)N NMR spectroscopy. (15)N spin-lattice relaxation rate constants (R(1)), spin-spin relaxation rate constants (R(2)), and steady-state heteronuclear (1)H-(15)N NOEs have been determined for 69 of the 86 (excluding two prolines and the N-terminal residue) backbone amide (15)N at a magnetic field strength of 14.1 Tesla. The primary relaxation data have been analyzed by using the model-free formalism of molecular dynamics, using both isotropic and axially symmetric diffusion of the molecule, to determine the overall rotational correlation time (tau(m)), the generalized order parameter (S(2)), the effective correlation time for internal motions (tau(e)), and NH exchange broadening contributions (R(ex)) for each residue. As per the axially symmetric diffusion, the ratio of diffusion rates about the unique and perpendicular axes (D( parallel)/D( perpendicular)) is 0.82 +/- 0.03. The two results have only marginal differences. The relaxation data have also been used to map reduced spectral densities for the NH vectors of these residues at three frequencies: 0, omega(H), and omega(N), where omega(H),(N) are proton and nitrogen Larmor frequencies. The value of tau(m) obtained from model-free analysis of the relaxation data is 5.2 ns. The reduced spectral density analysis, however, yields a value of 5.7 ns. The tau(m) determined here is different from that calculated previously from time-resolved fluorescence data (4.1 ns). The order parameter ranges from 0.68 to 0.98, with an average value of 0.85 +/- 0.02. A comparison of the order parameters with the X-ray B-factors for the backbone nitrogens of wild-type barstar does not show any considerable correlation. Model-free analysis of the relaxation data for seven residues required the inclusion of an exchange broadening term, the magnitude of which ranges from 2

  5. 15N-15N Proton Assisted Recoupling in Magic Angle Spinning NMR

    PubMed Central

    Lewandowski, Józef R.; De Paëpe, Gaël; Eddy, Matthew T.; Griffin, Robert G.

    2009-01-01

    We describe a new magic angle spinning (MAS) NMR experiment for obtaining 15N-15N correlation spectra. The approach yields direct information about the secondary and tertiary structure of proteins, including identification of α-helical stretches and inter-strand connectivity in antiparallel β-sheets, which are of major interest for structural studies of membrane proteins and amyloid fibrils. The method, 15N-15N proton assisted recoupling (PAR), relies on a second order mechanism, third spin assisted recoupling (TSAR), used previously in the context of 15N-13C and 13C-13C polarization transfer schemes. In comparison to 15N-15N proton driven spin diffusion experiments, the PAR technique accelerates polarization transfer between 15N’s by a factor of ~102−103, and is furthermore applicable over the entire range of currently available MAS frequencies (10–70 kHz). PMID:19334788

  6. Slow motions in microcrystalline proteins as observed by MAS-dependent 15N rotating-frame NMR relaxation

    NASA Astrophysics Data System (ADS)

    Krushelnitsky, Alexey; Zinkevich, Tatiana; Reif, Bernd; Saalwächter, Kay

    2014-11-01

    15N NMR relaxation rate R1ρ measurements reveal that a substantial fraction of residues in the microcrystalline chicken alpha-spectrin SH3 domain protein undergoes dynamics in the μs-ms timescale range. On the basis of a comparison of 2D site-resolved with 1D integrated 15N spectral intensities, we demonstrate that the significant fraction of broad signals in the 2D spectrum exhibits the most pronounced slow mobility. We show that 15N R1ρ's in proton-diluted protein samples are practically free from the coherent spin-spin contribution even at low MAS rates, and thus can be analysed quantitatively. Moderate MAS rates (10-30 kHz) can be more advantageous in comparison with the rates >50-60 kHz when slow dynamics are to be identified and quantified by means of R1ρ experiments.

  7. Proton-decoupled CPMG: a better experiment for measuring (15)N R2 relaxation in disordered proteins.

    PubMed

    Yuwen, Tairan; Skrynnikov, Nikolai R

    2014-04-01

    (15)N R2 relaxation is one of the most informative experiments for characterization of intrinsically disordered proteins (IDPs). Small changes in nitrogen R2 rates are often used to determine how IDPs respond to various biologically relevant perturbations such as point mutations, posttranslational modifications and weak ligand interactions. However collecting high-quality (15)N relaxation data can be difficult. Of necessity, the samples of IDPs are often prepared with low protein concentration and the measurement time can be limited because of rapid sample degradation. Furthermore, due to hardware limitations standard experiments such as (15)N spin-lock and CPMG can sample the relaxation decay only to ca. 150ms. This is much shorter than (15)N T2 times in disordered proteins at or near physiological temperature. As a result, the sampling of relaxation decay profiles in these experiments is suboptimal, which further lowers the precision of the measurements. Here we report a new implementation of the proton-decoupled (PD) CPMG experiment which allows one to sample (15)N R2 relaxation decay up to ca. 0.5-1s. The new experiment has been validated through comparison with the well-established spin-lock measurement. Using dilute samples of denatured ubiquitin, we have demonstrated that PD-CPMG produces up to 3-fold improvement in the precision of the data. It is expected that for intrinsically disordered proteins the gains may be even more substantial. We have also shown that this sequence has a number of favorable properties: (i) the spectra are recorded with narrow linewidth in nitrogen dimension; (ii) (15)N offset correction is small and easy to calculate; (iii) the experiment is immune to various spurious effects arising from solvent exchange; (iv) the results are stable with respect to pulse miscalibration and rf field inhomogeneity; (v) with minimal change, the pulse sequence can also be used to measure R2 relaxation of (15)N(ε) spins in arginine side chains. We

  8. Anisotropic spin relaxation in graphene.

    PubMed

    Tombros, N; Tanabe, S; Veligura, A; Jozsa, C; Popinciuc, M; Jonkman, H T; van Wees, B J

    2008-07-25

    Spin relaxation in graphene is investigated in electrical graphene spin valve devices in the nonlocal geometry. Ferromagnetic electrodes with in-plane magnetizations inject spins parallel to the graphene layer. They are subject to Hanle spin precession under a magnetic field B applied perpendicular to the graphene layer. Fields above 1.5 T force the magnetization direction of the ferromagnetic contacts to align to the field, allowing injection of spins perpendicular to the graphene plane. A comparison of the spin signals at B=0 and B=2 T shows a 20% decrease in spin relaxation time for spins perpendicular to the graphene layer compared to spins parallel to the layer. We analyze the results in terms of the different strengths of the spin-orbit effective fields in the in-plane and out-of-plane directions and discuss the role of the Elliott-Yafet and Dyakonov-Perel mechanisms for spin relaxation. PMID:18764351

  9. Nitrogen-15 spin-rotation relaxation in ammonium perchlorate

    NASA Astrophysics Data System (ADS)

    Harnden, Anne M. C.; Hunter, Brian K.; Brown, R. Julian C.

    The spin-lattice relaxation time has been measured for 15N in ammonium perchlorate in the temperature range 240 to 292 K. The temperature dependence of T, suggests that spin-rotation is the dominant relaxation mechanism, and this is confirmed by calculation and by nuclear Overhauser effect measurements. The spin-rotation coupling constant for 15NH 4+ is estimated to be 11.1 ± 0.2 kHz.

  10. Unraveling the complexity of protein backbone dynamics with combined (13)C and (15)N solid-state NMR relaxation measurements.

    PubMed

    Lamley, Jonathan M; Lougher, Matthew J; Sass, Hans Juergen; Rogowski, Marco; Grzesiek, Stephan; Lewandowski, Józef R

    2015-09-14

    Typically, protein dynamics involve a complex hierarchy of motions occurring on different time scales between conformations separated by a range of different energy barriers. NMR relaxation can in principle provide a site-specific picture of both the time scales and amplitudes of these motions, but independent relaxation rates sensitive to fluctuations in different time scale ranges are required to obtain a faithful representation of the underlying dynamic complexity. This is especially pertinent for relaxation measurements in the solid state, which report on dynamics in a broader window of time scales by more than 3 orders of magnitudes compared to solution NMR relaxation. To aid in unraveling the intricacies of biomolecular dynamics we introduce (13)C spin-lattice relaxation in the rotating frame (R1ρ) as a probe of backbone nanosecond-microsecond motions in proteins in the solid state. We present measurements of (13)C'R1ρ rates in fully protonated crystalline protein GB1 at 600 and 850 MHz (1)H Larmor frequencies and compare them to (13)C'R1, (15)N R1 and R1ρ measured under the same conditions. The addition of carbon relaxation data to the model free analysis of nitrogen relaxation data leads to greatly improved characterization of time scales of protein backbone motions, minimizing the occurrence of fitting artifacts that may be present when (15)N data is used alone. We also discuss how internal motions characterized by different time scales contribute to (15)N and (13)C relaxation rates in the solid state and solution state, leading to fundamental differences between them, as well as phenomena such as underestimation of picosecond-range motions in the solid state and nanosecond-range motions in solution.

  11. Spin Relaxation and Spin Transport in Graphene

    NASA Astrophysics Data System (ADS)

    Wu, M. W.

    2012-02-01

    In this talk we are going to present our theoretical investigations on spin dynamics of graphene under various conditions based on a fully microscopic kinetic-spin-Bloch-equation approach [1]. We manage to nail down the solo spin relaxation mechanism of graphene in measurements from two leading groups, one in US and one in the Netherland. Many novel effects of the electron-electron Coulomb interaction on spin relaxation in graphene are addressed. Our theory can have nice agreement with experimental data.[4pt] [1] M. W. Wu, J. H. Jiang, and M. Q. Weng, ``Spin dynamics in semiconductors,'' Phys. Rep. 493, 61 (2010).

  12. Backbone dynamics of free barnase and its complex with barstar determined by 15N NMR relaxation study.

    PubMed

    Sahu, S C; Bhuyan, A K; Udgaonkar, J B; Hosur, R V

    2000-10-01

    Backbone dynamics of uniformly 15N-labeled free barnase and its complex with unlabelled barstar have been studied at 40 degrees C, pH 6.6, using 15N relaxation data obtained from proton-detected 2D [1H]-15N NMR spectroscopy. 15N spin-lattice relaxation rate constants (R1), spin-spin relaxation rate constants (R2), and steady-state heteronuclear [1H]-15N NOEs have been measured at a magnetic field strength of 14.1 Tesla for 91 residues of free barnase and for 90 residues out of a total of 106 in the complex (excluding three prolines and the N-terminal residue) backbone amide 15N sites of barnase. The primary relaxation data for both the cases have been analyzed in the framework of the model-free formalism using both isotropic and axially symmetric models of the rotational diffusion tensor. As per the latter, the overall rotational correlation times (tau(m)) are 5.0 and 9.5 ns for the free and complexed barnase, respectively. The average order parameter is found to be 0.80 for free barnase and 0.86 for the complex. However, the changes are not uniform along the backbone and for about 5 residues near the binding interface there is actually a significant decrease in the order parameters on complex formation. These residues are not involved in the actual binding. For the residues where the order parameter increases, the magnitudes vary significantly. It is observed that the complex has much less internal mobility, compared to free barnase. From the changes in the order parameters, the entropic contribution of NH bond vector motion to the free energy of complex formation has been calculated. It is apparent that these motion's cause significant unfavorable contributions and therefore must be compensated by many other favorable contributions to effect tight complex formation. The observed variations in the motion and their different locations with regard to the binding interface may have important implications for remote effects and regulation of the enzyme action. PMID

  13. Variability of the 15N Chemical Shielding Tensors in the B3 Domain of Protein G from 15N Relaxation Measurements at Several Fields

    PubMed Central

    Hall, Jennifer B.; Fushman, David

    2008-01-01

    We applied a combination of 15N relaxation and CSA/dipolar cross-correlation measurements at five magnetic fields (9.4, 11.7, 14.1, 16.4, and 18.8 Tesla) to determine the 15N chemical shielding tensors for backbone amides in protein G in solution. The data were analyzed using various model-independent approaches and those based on Lipari-Szabo approximation, all of them yielding similar results. The results indicate a range of site-specific values of the anisotropy (CSA) and orientation of the 15N chemical shielding tensor, similar to those in ubiquitin. Assuming a Gaussian distribution of the 15N CSA values, the mean anisotropy is -173.9 to -177.2 ppm (for 1.02-Å NH-bond length) and the site-so-site CSA variability is ±17.6 to ±21.4 ppm, depending on the method used. This CSA variability is significantly larger than derived previously for ribonuclease H or recently, using “meta-analysis” for ubiquitin. Standard interpretation of 15N relaxation studies of backbone dynamics in proteins involves an a priori assumption of a uniform 15N CSA. We show that this assumption leads to a significant discrepancy between the order parameters obtained at different fields. Using the site-specific CSAs obtained from our study removes this discrepancy and allows simultaneous fit of relaxation data at all five fields to Lipari-Szabo spectral densities. These findings emphasize the necessity of taking into account the variability of 15N CSA for accurate analysis of protein dynamics from 15N relaxation measurements. PMID:16771499

  14. Distinguishing spin relaxation mechanisms in organic semiconductors.

    PubMed

    Harmon, N J; Flatté, M E

    2013-04-26

    A theory is introduced for spin relaxation and spin diffusion of hopping carriers in a disordered system. For disorder described by a distribution of waiting times between hops (e.g., from multiple traps, site-energy disorder, and/or positional disorder) the dominant spin relaxation mechanisms in organic semiconductors (hyperfine, hopping-induced spin-orbit, and intrasite spin relaxation) each produce different characteristic spin relaxation and spin diffusion dependences on temperature. The resulting unique experimental signatures predicted by the theory for each mechanism in organic semiconductors provide a prescription for determining the dominant spin relaxation mechanism. PMID:23679752

  15. Spin relaxation in disordered media

    NASA Astrophysics Data System (ADS)

    Dzheparov, F. S.

    2011-10-01

    A review is given on theoretical grounds and typical experimental appearances of spin dynamics and relaxation in solids containing randomly distributed nuclear and/or electronic spins. Brief content is as follows. Disordered and magnetically diluted systems. General outlines of the spin transport theory. Random walks in disordered systems (RWDS). Observable values in phase spin relaxation, free induction decay (FID). Interrelation of longitudinal and transversal relaxation related to dynamics of occupancies and phases. Occupation number representation for equations of motion. Continuum media approximation and inapplicability of moment expansions. Long-range transitions vs percolation theory. Concentration expansion as a general constructive basis for analytical methods. Scaling properties of propagators. Singular point. Dynamical and kinematical memory in RWDS. Ways of regrouping of concentration expansions. CTRW and semi-phenomenology. Coherent medium approximation for nuclear relaxation via paramagnetic impurities. Combining of memory functions and cumulant expansions for calculation of FID. Path integral representations for RWDS. Numerical simulations of RWDS. Spin dynamics in magnetically diluted systems with low Zeeman and medium low dipole temperatures. Cluster expansions, regularization of dipole interactions and spectral dynamics.

  16. The effect of noncollinearity of 15N-1H dipolar and 15N CSA tensors and rotational anisotropy on 15N relaxation, CSA/dipolar cross correlation, and TROSY.

    PubMed

    Fushman, D; Cowburn, D

    1999-02-01

    Current approaches to 15N relaxation in proteins assume that the 15N-1H dipolar and 15N CSA tensors are collinear. We show theoretically that, when there is significant anisotropy of molecular rotation, different orientations of the two tensors, experimentally observed in proteins, nucleic acids, and small peptides, will result in differences in site-specific correlation functions and spectral densities. The standard treatments of the rates of longitudinal and transverse relaxation of amide 15N nuclei, of the 15N CSA/15N-1H dipolar cross correlation, and of the TROSY experiment are extended to account for the effect of noncollinearity of the 15N-1H dipolar and 15N CSA (chemical shift anisotropy) tensors. This effect, proportional to the degree of anisotropy of the overall motion, (D parallel/D perpendicular - 1), is sensitive to the relative orientation of the two tensors and to the orientation of the peptide plane with respect to the diffusion coordinate frame. The effect is negligible at small degrees of anisotropy, but is predicted to become significant for D parallel/D perpendicular > or = 1.5, and at high magnetic fields. The effect of noncollinearity of 15N CSA and 15N-1H dipolar interaction is sensitive to both gross (hydrodynamic) properties and atomic-level details of protein structure. Incorporation of this effect into relaxation data analysis is likely to improve both precision and accuracy of the derived characteristics of protein dynamics, especially at high magnetic fields and for molecules with a high degree of anisotropy of the overall motion. The effect will also make TROSY efficiency dependent on local orientation in moderately anisotropic systems.

  17. 15N-15N spin-spin coupling constants through intermolecular hydrogen bonds in the solid state.

    PubMed

    Claramunt, Rosa M; Pérez-Torralba, Marta; María, Dolores Santa; Sanz, Dionisia; Elena, Bénédicte; Alkorta, Ibon; Elguero, José

    2010-10-01

    A 2hJNN intermolecular spin-spin coupling constant (SSCC) of 10.2±0.4 Hz has been measured for the powdered tetrachlorogallate salt of pyridinium solvated by pyridine (pyridine-H+⋯pyridine cation 3). Density Functional Theory (DFT) calculations at the B3LYP/6-311++G(d,p) level reproduced this value and two others reported in the literature for 2hJ intermolecular SSCCs, which were measured for complexes in solution.

  18. Spin relaxation in metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Berger, L.

    2011-02-01

    The Elliott theory of spin relaxation in metals and semiconductors is extended to metallic ferromagnets. Our treatment is based on the two-current model of Fert, Campbell, and Jaoul. The d→s electron-scattering process involved in spin relaxation is the inverse of the s→d process responsible for the anisotropic magnetoresistance (AMR). As a result, spin-relaxation rate 1/τsr and AMR Δρ are given by similar formulas, and are in a constant ratio if scattering is by solute atoms. Our treatment applies to nickel- and cobalt-based alloys which do not have spin-up 3d states at the Fermi level. This category includes many of the technologically important magnetic materials. And we show how to modify the theory to apply it to bcc iron-based alloys. We also treat the case of Permalloy Ni80Fe20 at finite temperature or in thin-film form, where several kinds of scatterers exist. Predicted values of 1/τsr and Δρ are plotted versus resistivity of the sample. These predictions are compared to values of 1/τsr and Δρ derived from ferromagnetic-resonance and AMR experiments in Permalloy.

  19. Toward hyperpolarized molecular imaging of HIV: synthesis and longitudinal relaxation properties of 15N-Azidothymidine

    PubMed Central

    Shchepin, Roman V.; Chekmenev, Eduard Y.

    2015-01-01

    Previously unreported 15N labeled Azidothymidine (AZT) was prepared as an equimolar mixture of two isotopomers: 1-15N-AZT and 3-15N-AZT. Polarization decay of 15N NMR signal was studied in high (9.4 T) and low (~50 mT) magnetic fields. 15N T1 values were 45 ± 5 s (1-15N-AZT) and 37 ± 2 s (3-15N-AZT) at 9.4 T, and 140 ± 16 s (3-15N-AZT) at 50 mT. 15N-AZT can be potentially 15N hyperpolarized by several methods. These sufficiently long 15N-AZT T1 values potentially enable hyperpolarized in vivo imaging of 15N-AZT, because of the known favorable efficient (i.e., of the time scale shorter than the longest reported here 15N T1) kinetics of uptake of injected AZT. Therefore, 3-15N-AZT can be potentially used for HIV molecular imaging using hyperpolarized magnetic resonance imaging. PMID:25156931

  20. Backbone dynamics of the oligomerization domain of p53 determined from 15N NMR relaxation measurements.

    PubMed

    Clubb, R T; Omichinski, J G; Sakaguchi, K; Appella, E; Gronenborn, A M; Clore, G M

    1995-05-01

    The backbone dynamics of the tetrameric p53 oligomerization domain (residues 319-360) have been investigated by two-dimensional inverse detected heteronuclear 1H-15N NMR spectroscopy at 500 and 600 MHz. 15N T1, T2, and heteronuclear NOEs were measured for 39 of 40 non-proline backbone NH vectors at both field strengths. The overall correlation time for the tetramer, calculated from the T1/T2 ratios, was found to be 14.8 ns at 35 degrees C. The correlation times and amplitudes of the internal motions were extracted from the relaxation data using the model-free formalism (Lipari G, Szabo A, 1982, J Am Chem Soc 104:4546-4559). The internal dynamics of the structural core of the p53 oligomerization domain are uniform and fairly rigid, with residues 327-354 exhibiting an average generalized order parameter (S2) of 0.88 +/- 0.08. The N- and C-termini exhibit substantial mobility and are unstructured in the solution structure of p53. Residues located at the N- and C-termini, in the beta-sheet, in the turn between the alpha-helix and beta-sheet, and at the C-terminal end of the alpha-helix display two distinct internal motions that are faster than the overall correlation time. Fast internal motions (< or = 20 ps) are within the extreme narrowing limit and are of uniform amplitude. The slower motions (0.6-2.2 ns) are outside the extreme narrowing limit and vary in amplitude.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7663341

  1. Spin-orbit coupling and spin relaxation in phosphorene

    NASA Astrophysics Data System (ADS)

    Kurpas, Marcin; Gmitra, Martin; Fabian, Jaroslav

    We employ first principles density functional theory calculations to study intrinsic and extrinsic spin-orbit coupling in monolayer phosphorene. We also extract the spin-mixing amplitudes of the Bloch wave functions to give realistic estimates of the Elliott-Yafet spin relaxation rate. The most remarkable result is the striking anisotropy in both spin-orbit coupling and spin relaxation rates, which could be tested experimentally in spin injection experiments. We also identify spin hot spots in the electronic structure of phosphorene at accidental bands anticrossings. We compare the Elliott-Yafet with Dyakonov-Perel spin relaxation times, obtained from extrinsic couplings in an applied electric field. We also compare the results in phosphorene with those of black phosphorous. This work is supported by the DFG SPP 1538, SFB 689, and by the EU Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship.

  2. Doppler effect induced spin relaxation boom

    PubMed Central

    Zhao, Xinyu; Huang, Peihao; Hu, Xuedong

    2016-01-01

    We study an electron spin qubit confined in a moving quantum dot (QD), with our attention on both spin relaxation, and the product of spin relaxation, the emitted phonons. We find that Doppler effect leads to several interesting phenomena. In particular, spin relaxation rate peaks when the QD motion is in the transonic regime, which we term a spin relaxation boom in analogy to the classical sonic boom. This peak indicates that a moving spin qubit may have even lower relaxation rate than a static qubit, pointing at the possibility of coherence-preserving transport for a spin qubit. We also find that the emitted phonons become strongly directional and narrow in their frequency range as the qubit reaches the supersonic regime, similar to Cherenkov radiation. In other words, fast moving excited spin qubits can act as a source of non-classical phonons. Compared to classical Cherenkov radiation, we show that quantum dot confinement produces a small but important correction on the Cherenkov angle. Taking together, these results have important implications to both spin-based quantum information processing and coherent phonon dynamics in semiconductor nanostructures. PMID:26996253

  3. Doppler effect induced spin relaxation boom.

    PubMed

    Zhao, Xinyu; Huang, Peihao; Hu, Xuedong

    2016-03-21

    We study an electron spin qubit confined in a moving quantum dot (QD), with our attention on both spin relaxation, and the product of spin relaxation, the emitted phonons. We find that Doppler effect leads to several interesting phenomena. In particular, spin relaxation rate peaks when the QD motion is in the transonic regime, which we term a spin relaxation boom in analogy to the classical sonic boom. This peak indicates that a moving spin qubit may have even lower relaxation rate than a static qubit, pointing at the possibility of coherence-preserving transport for a spin qubit. We also find that the emitted phonons become strongly directional and narrow in their frequency range as the qubit reaches the supersonic regime, similar to Cherenkov radiation. In other words, fast moving excited spin qubits can act as a source of non-classical phonons. Compared to classical Cherenkov radiation, we show that quantum dot confinement produces a small but important correction on the Cherenkov angle. Taking together, these results have important implications to both spin-based quantum information processing and coherent phonon dynamics in semiconductor nanostructures.

  4. Doppler effect induced spin relaxation boom

    NASA Astrophysics Data System (ADS)

    Zhao, Xinyu; Huang, Peihao; Hu, Xuedong

    2016-03-01

    We study an electron spin qubit confined in a moving quantum dot (QD), with our attention on both spin relaxation, and the product of spin relaxation, the emitted phonons. We find that Doppler effect leads to several interesting phenomena. In particular, spin relaxation rate peaks when the QD motion is in the transonic regime, which we term a spin relaxation boom in analogy to the classical sonic boom. This peak indicates that a moving spin qubit may have even lower relaxation rate than a static qubit, pointing at the possibility of coherence-preserving transport for a spin qubit. We also find that the emitted phonons become strongly directional and narrow in their frequency range as the qubit reaches the supersonic regime, similar to Cherenkov radiation. In other words, fast moving excited spin qubits can act as a source of non-classical phonons. Compared to classical Cherenkov radiation, we show that quantum dot confinement produces a small but important correction on the Cherenkov angle. Taking together, these results have important implications to both spin-based quantum information processing and coherent phonon dynamics in semiconductor nanostructures.

  5. Doppler effect induced spin relaxation boom.

    PubMed

    Zhao, Xinyu; Huang, Peihao; Hu, Xuedong

    2016-01-01

    We study an electron spin qubit confined in a moving quantum dot (QD), with our attention on both spin relaxation, and the product of spin relaxation, the emitted phonons. We find that Doppler effect leads to several interesting phenomena. In particular, spin relaxation rate peaks when the QD motion is in the transonic regime, which we term a spin relaxation boom in analogy to the classical sonic boom. This peak indicates that a moving spin qubit may have even lower relaxation rate than a static qubit, pointing at the possibility of coherence-preserving transport for a spin qubit. We also find that the emitted phonons become strongly directional and narrow in their frequency range as the qubit reaches the supersonic regime, similar to Cherenkov radiation. In other words, fast moving excited spin qubits can act as a source of non-classical phonons. Compared to classical Cherenkov radiation, we show that quantum dot confinement produces a small but important correction on the Cherenkov angle. Taking together, these results have important implications to both spin-based quantum information processing and coherent phonon dynamics in semiconductor nanostructures. PMID:26996253

  6. Controlling spin relaxation with a cavity.

    PubMed

    Bienfait, A; Pla, J J; Kubo, Y; Zhou, X; Stern, M; Lo, C C; Weis, C D; Schenkel, T; Vion, D; Esteve, D; Morton, J J L; Bertet, P

    2016-03-01

    Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the rate of spontaneous emission can be greatly enhanced by placing the quantum system in a resonant cavity. This effect has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, and is essential for the realization of high-efficiency single-photon sources. Here we report the application of this idea to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity with a high quality factor and a small mode volume, we reach the regime in which spontaneous emission constitutes the dominant mechanism of spin relaxation. The relaxation rate is increased by three orders of magnitude as the spins are tuned to the cavity resonance, demonstrating that energy relaxation can be controlled on demand. Our results provide a general way to initialize spin systems into their ground state and therefore have applications in magnetic resonance and quantum information processing. They also demonstrate that the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point at which quantum fluctuations have a marked effect on the spin dynamics; as such, they represent an important step towards the coherent magnetic coupling of individual spins to microwave photons. PMID:26878235

  7. A 15N CPMG relaxation dispersion experiment more resistant to resonance offset and pulse imperfection

    NASA Astrophysics Data System (ADS)

    Jiang, Bin; Yu, Binhan; Zhang, Xu; Liu, Maili; Yang, Daiwen

    2015-08-01

    Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion is a powerful NMR method to study protein dynamics on the microsecond-millisecond time scale. J-coupling, resonance offset, radio frequency field inhomogeneity, and pulse imperfection often introduce systematic errors into the measured transverse relaxation rates. Here we proposed a modified continuous wave decoupling CPMG experiment, which is more unaffected by resonance offset and pulse imperfection. We found that it is unnecessary to match the decoupling field strength with the delay between CPMG refocusing pulses, provided that decoupling field is strong enough. The performance of the scheme proposed here was shown by simulations and further demonstrated experimentally on a fatty acid binding protein.

  8. Theory of spin relaxation at metallic interfaces

    NASA Astrophysics Data System (ADS)

    Belashchenko, K. D.; Kovalev, Alexey A.; van Schilfgaarde, Mark

    Spin-flip scattering at metallic interfaces affects transport phenomena in nanostructures, such as magnetoresistance, spin injection, spin pumping, and spin torques. It has been characterized for many material combinations by an empirical parameter δ, which is obtained by matching magnetoresistance data for multilayers to the Valet-Fert model [J. Bass and W. P. Pratt, J. Phys.: Condens. Matter 19, 183201 (2007)]. However, the relation of the parameter δ to the scattering properties of the interface remains unclear. Here we establish this relation using the scattering theory approach and confirm it using a generalization of the magnetoelectronic circuit theory, which includes interfacial spin relaxation. The results of first-principles calculations of spin-flip scattering at the Cu/Pd and Cu/Pt interfaces are found to be in reasonable agreement with experimental data. Supported by NSF Grant DMR-1308751.

  9. Sensitivity enhancement and low-field spin relaxation in singlet NMR.

    PubMed

    Bocan, Jiri; Pileio, Giuseppe; Levitt, Malcolm H

    2012-12-14

    The singlet states of nuclear spin-1/2 pairs often display extended lifetimes that can be an order of magnitude longer than conventional relaxation times. We show that, in favourable circumstances, acquisition of the NMR signal during an extended multiple spin-echo train, followed by suitable data processing, enhances the signal-to-noise ratio of singlet NMR by up to an order of magnitude. The achievable enhancement depends on the transverse relaxation time constant, the magnetic field inhomogeneity, and the acceptable degradation in digital spectral resolution. We use the combination of singlet NMR and multiple spin-echo data acquisition to study the low-field nuclear relaxation processes of (15)N-labelled nitrous oxide ((15)N(2)O) in solution. A general relaxation theory for coupled 2-spin-1/2 systems in low magnetic field is developed. Experimental trajectories of the nuclear spin observables are compared with theoretical expressions, including dipole-dipole and spin-rotation relaxation mechanisms. The estimated values of the spin-rotation tensors are compared with previous estimations from NMR and molecular beam electric resonance.

  10. A (15)N CPMG relaxation dispersion experiment more resistant to resonance offset and pulse imperfection.

    PubMed

    Jiang, Bin; Yu, Binhan; Zhang, Xu; Liu, Maili; Yang, Daiwen

    2015-08-01

    Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion is a powerful NMR method to study protein dynamics on the microsecond-millisecond time scale. J-coupling, resonance offset, radio frequency field inhomogeneity, and pulse imperfection often introduce systematic errors into the measured transverse relaxation rates. Here we proposed a modified continuous wave decoupling CPMG experiment, which is more unaffected by resonance offset and pulse imperfection. We found that it is unnecessary to match the decoupling field strength with the delay between CPMG refocusing pulses, provided that decoupling field is strong enough. The performance of the scheme proposed here was shown by simulations and further demonstrated experimentally on a fatty acid binding protein. PMID:26037134

  11. Spin-Lattice Relaxation Times in 1H NMR Spectroscopy.

    ERIC Educational Resources Information Center

    Wink, Donald J.

    1989-01-01

    Discussed are the mechanisms of nuclear magnetic relaxation, and applications of relaxation times. The measurement of spin-lattice relaxations is reviewed. It is stressed that sophisticated techniques such as these are becoming more important to the working chemist. (CW)

  12. Muon spin relaxation in spin glass PdMn

    SciTech Connect

    Heffner, R.H.; Leon, M.; Schillaci, M.E.; Dodds, S.A.; Gist, G.A.; MacLaughlin, D.E.; Mydosh, J.A.; Nieuwenhuys, G.J.

    1983-01-01

    Muon spin relaxation (..mu..SR) rates have been measured in transverse, longitudinal, and zero applied field for the spin glass PdMn (7 at. %), and are compared with a previous study of the disordered ferromagnet PdMn (2 at. %). The calculated paramagnetic state transverse field relaxation rate for noninteracting spins is much larger than the observed rate in spin glass PdMn, but is in good agreement with ferromagnetic PdMn. The zero field relaxation rate shows a sharp cusp at T/sub g/=5K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glss PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below T/sub g/=5K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glass PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below T/sub g/, a distribution of quasistatic local fields is observed in zero field, which has the same temperature dependence for both samples. Comparisons with model calculations are discussed.

  13. Theory of the spin relaxation of conduction electrons in silicon.

    PubMed

    Cheng, J L; Wu, M W; Fabian, J

    2010-01-01

    A realistic pseudopotential model is introduced to investigate the phonon-induced spin relaxation of conduction electrons in bulk silicon. We find a surprisingly subtle interference of the Elliott and Yafet processes affecting the spin relaxation over a wide temperature range, suppressing the significance of the intravalley spin-flip scattering, previously considered dominant, above roughly 120 K. The calculated spin relaxation times T1 agree with the spin resonance and spin injection data, following a T(-3) temperature dependence. The valley anisotropy of T1 and the spin relaxation rates for hot electrons are predicted.

  14. Quantitative analysis of conformational exchange contributions to 1H-15N multiple-quantum relaxation using field-dependent measurements. Time scale and structural characterization of exchange in a calmodulin C-terminal domain mutant.

    PubMed

    Lundström, Patrik; Akke, Mikael

    2004-01-28

    Multiple-quantum spin relaxation is a sensitive probe for correlated conformational exchange dynamics on microsecond to millisecond time scales in biomolecules. We measured differential 1H-15N multiple-quantum relaxation rates for the backbone amide groups of the E140Q mutant of the C-terminal domain of calmodulin at three static magnetic field strengths. The differential multiple-quantum relaxation rates range between -88.7 and 92.7 s(-1), and the mean and standard deviation are 7.0 +/- 24 s(-1), at a static magnetic field strength of 14.1 T. Together with values of the 1H and 15N chemical shift anisotropies (CSA) determined separately, the field-dependent data enable separation of the different contributions from dipolar-dipolar, CSA-CSA, and conformational exchange cross-correlated relaxation mechanisms to the differential multiple-quantum relaxation rates. The procedure yields precise quantitative information on the dominant conformational exchange contributions observed in this protein. The field-dependent differences between double- and zero-quantum relaxation rates directly benchmark the rates of conformational exchange, showing that these are fast on the chemical shift time scale for the large majority of residues in the protein. Further analysis of the differential 1H-15N multiple-quantum relaxation rates using previously determined exchange rate constants and populations, obtained from 15N off-resonance rotating-frame relaxation data, enables extraction of the product of the chemical shift differences between the resonance frequencies of the 1H and 15N spins in the exchanging conformations, deltasigma(H)deltasigma(N). Thus, information on the 1H chemical shift differences is obtained, while circumventing complications associated with direct measurements of conformational exchange effects on 1H single-quantum coherences in nondeuterated proteins. The method significantly increases the information content available for structural interpretation of the

  15. Spin relaxation in geometrically frustrated pyrochlores

    NASA Astrophysics Data System (ADS)

    Dunsiger, Sarah Ruth

    This thesis describes muSR experiments which focus on systems where the magnetic ions occupy the vertices of edge or corner sharing triangular units, in particular the pyrochlores A2B2O7. The scientific interest in pyrochlores is based on the fact that they display novel magnetic behaviour at low temperatures due to geometrical frustration. The ground state of these systems is sensitively dependent on such factors as the range of the spin-spin interactions, disorder, anisotropy, thermal and quantum fluctuations. For example, Y2Mo2O7 shows many features reminiscent of a conventional spin glass, even though this material has nominally zero chemical disorder. It is found that the muon spin polarisation obeys a time-field scaling relation which indicates that the spin-spin autocorrelation function has a power law form in time, in stark contrast with the exponential form often assumed for conventional magnets above their transition temperature. Gd2Ti2O7 shows long range order, but only at a temperature much lower than its Curie-Weiss temperature, a signature of a frustrated system. In the paramagnetic regime, it is well described by an isotropic Heisenberg Hamiltonian with nearest neighbour couplings in the presence of a Zeeman interaction, from which the spin-spin autocorrelation function may be calculated as a power series in time. The muon spin relaxation rate decreases with magnetic field as the Zeeman energy becomes comparable with the exchange coupling between Gd spins. Thus, an independent measure of the exchange coupling or equivalently the Gd spin fluctuation rate is extracted. By contrast, Tb2Ti2O7 has been identified as a type of cooperative paramagnet. Short range correlations develop below 50 K. However, there is no long range ordering down to very low temperatures (0.075 K). The Tb3+ ion is subject to strong crystal electric field effects: point charge calculations indicate that this system is Ising like at low temperatures. Thus this system may be

  16. Characterization of the overall rotational diffusion of a protein from 15N relaxation measurements and hydrodynamic calculations.

    PubMed

    Blake-Hall, Jennifer; Walker, Oliver; Fushman, David

    2004-01-01

    In this chapter, we discuss experimental and theoretical methods for characterizing the overall rotational diffusion of molecules in solution. The methods are illustrated for the B3 domain of protein G, a small protein with rotational anisotropy of Dpar/Dperp = 1.4. The rotational diffusion tensor of the protein is determined directly from 15N relaxation measurements. The experimental data are treated assuming various possible models for the overall tumbling: isotropic, axially symmetric, and fully anisotropic, and the results of these analyses are compared to determine an adequate diffusion model for the protein. These experimentally derived characteristics of the protein are compared with the results of theoretical calculations of the diffusion tensor using various hydrodynamic models, to find optimal models and parameter sets for theoretical predictions. We also derive model-free characteristics of internal backbone motions in the protein, to show that different models for the overall motion can result in significantly different pictures of motion. This emphasizes the necessity of accurately characterizing the overall tumbling of a molecule to determine its local dynamics.

  17. Spin Waves and Spin Relaxation in Normal Fermi Liquids.

    NASA Astrophysics Data System (ADS)

    Meltzer, David Elliott

    This work explores several aspects of spin-dependent excitations in normal Fermi liquids. Chapter 1 is a general introduction and overview of the work. The Landau kinetic equation and its application to nonequilibrium proper- ties of Fermi liquids is discussed, and the properties of collective density modes are briefly reviewed. The properties of both longitu- dinal and transverse spin excitations are then outlined, leading up to a discussion of spin waves and spin diffusion, including the Leggett -Rice effect. Chapter 2 discusses the possibility of making a determination of the contribution of many-body interactions to the large effective mass in "heavy-fermion" materials, e.g. UPt(,3), by the method of conduction-electron spin resonance (CESR). It is shown that a microwave trans- mission observation of CESR might show a resonance pattern which, based on already measured parameters, would clearly distinguish among various suggested models for the strength of the many-body effects. Chapter 3 investigates the accuracy of the usual relaxation time approximations, involving the spin diffusion lifetime (tau)(,D), which are generally made in analyses of spin waves and the Leggett-Rice effect in Fermi liquids. By employing the variational methods of Ah-Sam, H(SLASHCIRC)jgaard -Jensen and Smith, and Egilsson and Pethick, we are able to determine upper and lower bounds on the effective diffusion coefficient resulting from spin wave phenomena which are accurate in the whole Fermi liquid regime. Our results indicate that the usual approximations break down for(' )T < 7 mK in ('3)He, but are accurate to within (TURN)2% in 5% ('3)He-('4)He mixtures. Chapter 4 contains a calculation of the longitudinal spin relaxa- tion time T(,1) in bulk ('3)He in the Fermi liquid (T << T(,F)) regime. The kinetic equation is used to obtain an expression for T(,1) in terms of perturbations of the scattering amplitude. These perturbations are then obtained using the induced interaction model

  18. Electron spin relaxation in carbon nanotubes: Dyakonov-Perel mechanism

    NASA Astrophysics Data System (ADS)

    Semenov, Yuriy; Zavada, John; Kim, Ki Wook

    2010-03-01

    The long standing problem of unaccountable short spin relaxation in carbon nanotubes (CNT) meets a disclosure in terms of curvature-mediated spin-orbital interaction that leads to spin fluctuating precession analogous to Dyakonov-Perel mechanism. Strong anisotropy imposed by arbitrary directed magnetic field has been taken into account in terms of extended Bloch equations. Especially, stationary spin current through CNT can be controlled by spin-flip processes with relaxation time as less as 150 ps, the rate of transversal polarization (i.e. decoherence) runs up to 1/(70 ps) at room temperature while spin interference of the electrons related to different valleys can be responsible for shorter spin dephasing. Dependencies of spin-relaxation parameters on magnetic field strength and orientation, CNT curvature and chirality have been analyzed.

  19. Spin relaxation of iron in mixed state hemoproteins.

    PubMed Central

    Wajnberg, E; Kalinowski, H J; Bemski, G; Helman, J S

    1986-01-01

    In hemoproteins the relaxation mechanism of iron is Orbach for high spin (HS) and Raman for low spin (LS). We found that in met-hemoglobin and met-myoglobin, under conditions in which the two spin states coexist, both the HS and the LS states relax to the lattice through Orbach-like processes. Alos, very short (approximately 1 ns) and temperature independent transverse relaxation times T2 were estimated. This may result from the unusual electronic structure of mixed states hemoproteins that allows thermal equilibrium and interconversion of the spin states. PMID:3013333

  20. Carbon relaxation analysis in proton coupled spin systems

    NASA Astrophysics Data System (ADS)

    Rossi, Claudio; Marchettini, Nadia; Bastianoni, Simone; Dongti, Alessandro

    1995-07-01

    Selective, non-selective and biselective carbon spin-lattice relaxation measurements were determined in methyl-salicylate DMSO-d 6 solution. The frequency dependence of biselective relaxation measurements of protonated aromatic carbons showed the effects of J-scalar modulation. The dipolar contribution induced by asymmetric selective proton inversion of the spin population of a single satellite peak could be useful for investigating of the Shimizu-Fujiwara-Mackor-Maclean relaxation rate. Analysis of the ratios is also proposed for the calculation of dipolar relaxation mechanism efficiency.

  1. PREFACE: Muon spin rotation, relaxation or resonance

    NASA Astrophysics Data System (ADS)

    Heffner, Robert H.; Nagamine, Kanetada

    2004-10-01

    To a particle physicist a muon is a member of the lepton family, a heavy electron possessing a mass of about 1/9 that of a proton and a spin of 1/2, which interacts with surrounding atoms and molecules electromagnetically. Since its discovery in 1937, the muon has been put to many uses, from tests of special relativity to deep inelastic scattering, from studies of nuclei to tests of weak interactions and quantum electrodynamics, and most recently, as a radiographic tool to see inside heavy objects and volcanoes. In 1957 Richard Garwin and collaborators, while conducting experiments at the Columbia University cyclotron to search for parity violation, discovered that spin-polarized muons injected into materials might be useful to probe internal magnetic fields. This eventually gave birth to the modern field of muSR, which stands for muon spin rotation, relaxation or resonance, and is the subject of this special issue of Journal of Physics: Condensed Matter. Muons are produced in accelerators when high energy protons (generally >500 MeV) strike a target like graphite, producing pions which subsequently decay into muons. Most experiments carried out today use relatively low-energy (~4 MeV), positively-charged muons coming from pions decaying at rest in the skin of the production target. These muons have 100% spin polarization, a range in typical materials of about 180 mg cm-2, and are ideal for experiments in condensed matter physics and chemistry. Negatively-charged muons are also occasionally used to study such things as muonic atoms and muon-catalysed fusion. The muSR technique provides a local probe of internal magnetic fields and is highly complementary to inelastic neutron scattering and nuclear magnetic resonance, for example. There are four primary muSR facilities in the world today: ISIS (Didcot, UK), KEK (Tsukuba, Japan), PSI (Villigen, Switzerland) and TRIUMF (Vancouver, Canada), serving about 500 researchers world-wide. A new facility, JPARC (Tokai, Japan

  2. PREFACE: Muon spin rotation, relaxation or resonance

    NASA Astrophysics Data System (ADS)

    Heffner, Robert H.; Nagamine, Kanetada

    2004-10-01

    To a particle physicist a muon is a member of the lepton family, a heavy electron possessing a mass of about 1/9 that of a proton and a spin of 1/2, which interacts with surrounding atoms and molecules electromagnetically. Since its discovery in 1937, the muon has been put to many uses, from tests of special relativity to deep inelastic scattering, from studies of nuclei to tests of weak interactions and quantum electrodynamics, and most recently, as a radiographic tool to see inside heavy objects and volcanoes. In 1957 Richard Garwin and collaborators, while conducting experiments at the Columbia University cyclotron to search for parity violation, discovered that spin-polarized muons injected into materials might be useful to probe internal magnetic fields. This eventually gave birth to the modern field of muSR, which stands for muon spin rotation, relaxation or resonance, and is the subject of this special issue of Journal of Physics: Condensed Matter. Muons are produced in accelerators when high energy protons (generally >500 MeV) strike a target like graphite, producing pions which subsequently decay into muons. Most experiments carried out today use relatively low-energy (~4 MeV), positively-charged muons coming from pions decaying at rest in the skin of the production target. These muons have 100% spin polarization, a range in typical materials of about 180 mg cm-2, and are ideal for experiments in condensed matter physics and chemistry. Negatively-charged muons are also occasionally used to study such things as muonic atoms and muon-catalysed fusion. The muSR technique provides a local probe of internal magnetic fields and is highly complementary to inelastic neutron scattering and nuclear magnetic resonance, for example. There are four primary muSR facilities in the world today: ISIS (Didcot, UK), KEK (Tsukuba, Japan), PSI (Villigen, Switzerland) and TRIUMF (Vancouver, Canada), serving about 500 researchers world-wide. A new facility, JPARC (Tokai, Japan

  3. Spin relaxation via exchange with donor impurity-bound electrons

    NASA Astrophysics Data System (ADS)

    Appelbaum, Ian

    In the Bir-Aronov-Pikus depolarization process affecting conduction electrons in p-type cubic semiconductors, spin relaxation is driven by exchange with short-lived valence band hole states. We have identified an analogous spin relaxation mechanism in nominally undoped silicon at low temperatures, when many electrons are bound to dilute dopant ion potentials. Inelastic scattering with externally injected conduction electrons accelerated by electric fields can excite transitions into highly spin-orbit-mixed bound excited states, driving strong spin relaxation of the conduction electrons via exchange interaction. We reveal the consequences of this spin depolarization mechanism both below and above the impact ionization threshold, where conventional charge and spin transport are restored. Based upon: Lan Qing, Jing Li, Ian Appelbaum, and Hanan Dery, Phys Rev. B 91, 241405(R) (2015). We acknowledge support from NSF, DTRA, and ONR.

  4. Spin Relaxation in Materials Lacking Coherent Charge Transport

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas

    2015-03-01

    As semiconductor spintronics research extends to materials beyond intrinsic or lightly doped semiconductors (e. g. organic materials, amorphous semiconductors, and impurity bands), the need is readily apparent for new theories of spin relaxation that encompass highly disordered materials, where charge transport is incoherent. We describe a broadly applicable theory of spin relaxation in materials with incoherent charge transport. The theory is based on continuous-time-random-walk theory and can incorporate many different relaxation mechanisms. We focus primarily on spin relaxation caused by spin-orbit and hyperfine effects in conjunction with carrier hopping. Analytic and numerical results from the theory are compared in various regimes with Monte Carlo simulations. Three different systems were examined: a polymer (MEH-PPV), amorphous silicon, and heavily doped n-GaAs. In the organic and amorphous systems, we predict spin relaxation and spin diffusion dependences on temperature and disorder for three different mechanisms (hyperfine, hopping-induced spin-orbit, and intra-site spin relaxation). The resulting unique experimental signatures predicted by the theory for each mechanism in these disordered systems provide a prescription for determining the dominant spin relaxation mechanism. We find our theory to be in agreement with available measurements in these materials. We also predict that large disorder modifies certain mechanisms to be algebraic instead of exponential in time. Our results should assist in evaluating the suitability of various disordered materials for spintronic devices. All work done in collaboration with Michael E. Flatté. Timothy Peterson and Paul Crowell collaborated as well on the n-GaAs study. This work was supported by an ARO MURI and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  5. Nanosecond spin relaxation times in single layer graphene spin valves with hexagonal boron nitride tunnel barriers

    NASA Astrophysics Data System (ADS)

    Singh, Simranjeet; Katoch, Jyoti; Xu, Jinsong; Tan, Cheng; Zhu, Tiancong; Amamou, Walid; Hone, James; Kawakami, Roland

    2016-09-01

    We present an experimental study of spin transport in single layer graphene using atomic sheets of hexagonal boron nitride (h-BN) as a tunnel barrier for spin injection. While h-BN is expected to be favorable for spin injection, previous experimental studies have been unable to achieve spin relaxation times in the nanosecond regime, suggesting potential problems originating from the contacts. Here, we investigate spin relaxation in graphene spin valves with h-BN barriers and observe room temperature spin lifetimes in excess of a nanosecond, which provides experimental confirmation that h-BN is indeed a good barrier material for spin injection into graphene. By carrying out measurements with different thicknesses of h-BN, we show that few layer h-BN is a better choice than monolayer for achieving high non-local spin signals and longer spin relaxation times in graphene.

  6. Electron spin relaxation in cryptochrome-based magnetoreception.

    PubMed

    Kattnig, Daniel R; Solov'yov, Ilia A; Hore, P J

    2016-05-14

    The magnetic compass sense of migratory birds is thought to rely on magnetically sensitive radical pairs formed photochemically in cryptochrome proteins in the retina. An important requirement of this hypothesis is that electron spin relaxation is slow enough for the Earth's magnetic field to have a significant effect on the coherent spin dynamics of the radicals. It is generally assumed that evolutionary pressure has led to protection of the electron spins from irreversible loss of coherence in order that the underlying quantum dynamics can survive in a noisy biological environment. Here, we address this question for a structurally characterized model cryptochrome expected to share many properties with the putative avian receptor protein. To this end we combine all-atom molecular dynamics simulations, Bloch-Redfield relaxation theory and spin dynamics calculations to assess the effects of spin relaxation on the performance of the protein as a compass sensor. Both flavin-tryptophan and flavin-Z˙ radical pairs are studied (Z˙ is a radical with no hyperfine interactions). Relaxation is considered to arise from modulation of hyperfine interactions by librational motions of the radicals and fluctuations in certain dihedral angles. For Arabidopsis thaliana cryptochrome 1 (AtCry1) we find that spin relaxation implies optimal radical pair lifetimes of the order of microseconds, and that flavin-Z˙ pairs are less affected by relaxation than flavin-tryptophan pairs. Our results also demonstrate that spin relaxation in isolated AtCry1 is incompatible with the long coherence times that have been postulated to explain the disruption of the avian magnetic compass sense by weak radiofrequency magnetic fields. We conclude that a cryptochrome sensor in vivo would have to differ dynamically, if not structurally, from isolated AtCry1. Our results clearly mark the limits of the current hypothesis and lead to a better understanding of the operation of radical pair magnetic sensors

  7. Electron spin dynamics and spin-lattice relaxation of trityl radicals in frozen solutions.

    PubMed

    Chen, Hanjiao; Maryasov, Alexander G; Rogozhnikova, Olga Yu; Trukhin, Dmitry V; Tormyshev, Victor M; Bowman, Michael K

    2016-09-28

    Electron spin-lattice relaxation of two trityl radicals, d24-OX063 and Finland trityl, were studied under conditions relevant to their use in dissolution dynamic nuclear polarization (DNP). The dependence of relaxation kinetics on temperature up to 100 K and on concentration up to 60 mM was obtained at X- and W-bands (0.35 and 3.5 Tesla, respectively). The relaxation is quite similar at both bands and for both trityl radicals. At concentrations typical for DNP, relaxation is mediated by excitation transfer and spin-diffusion to fast-relaxing centers identified as triads of trityl radicals that spontaneously form in the frozen samples. These centers relax by an Orbach-Aminov mechanism and determine the relaxation, saturation and electron spin dynamics during DNP. PMID:27560644

  8. Local Spin Relaxation within the Random Heisenberg Chain

    NASA Astrophysics Data System (ADS)

    Herbrych, J.; Kokalj, J.; Prelovšek, P.

    2013-10-01

    Finite-temperature local dynamical spin correlations Snn(ω) are studied numerically within the random spin-1/2 antiferromagnetic Heisenberg chain. The aim is to explain measured NMR spin-lattice relaxation times in BaCu2(Si0.5Ge0.5)2O7, which is the realization of a random spin chain. In agreement with experiments we find that the distribution of relaxation times within the model shows a very large span similar to the stretched-exponential form. The distribution is strongly reduced with increasing T, but stays finite also in the high-T limit. Anomalous dynamical correlations can be associated with the random singlet concept but not directly with static quantities. Our results also reveal the crucial role of the spin anisotropy (interaction), since the behavior is in contrast with the ones for the XX model, where we do not find any significant T dependence of the distribution.

  9. Donor-driven spin relaxation in multivalley semiconductors.

    PubMed

    Song, Yang; Chalaev, Oleg; Dery, Hanan

    2014-10-17

    The observed dependence of spin relaxation on the identity of the donor atom in n-type silicon has remained without explanation for decades and poses a long-standing open question with important consequences for modern spintronics. Taking into account the multivalley nature of the conduction band in silicon and germanium, we show that the spin-flip amplitude is dominated by short-range scattering off the central-cell potential of impurities after which the electron is transferred to a valley on a different axis in k space. Through symmetry arguments, we show that this spin-flip process can strongly affect the spin relaxation in all multivalley materials in which time-reversal cannot connect distinct valleys. From the physical insights gained from the theory, we provide guidelines to significantly enhance the spin lifetime in semiconductor spintronics devices. PMID:25361275

  10. Donor-driven spin relaxation in multivalley semiconductors.

    PubMed

    Song, Yang; Chalaev, Oleg; Dery, Hanan

    2014-10-17

    The observed dependence of spin relaxation on the identity of the donor atom in n-type silicon has remained without explanation for decades and poses a long-standing open question with important consequences for modern spintronics. Taking into account the multivalley nature of the conduction band in silicon and germanium, we show that the spin-flip amplitude is dominated by short-range scattering off the central-cell potential of impurities after which the electron is transferred to a valley on a different axis in k space. Through symmetry arguments, we show that this spin-flip process can strongly affect the spin relaxation in all multivalley materials in which time-reversal cannot connect distinct valleys. From the physical insights gained from the theory, we provide guidelines to significantly enhance the spin lifetime in semiconductor spintronics devices.

  11. Spin relaxation characteristics in Ag nanowire covered with various oxides

    SciTech Connect

    Karube, S.; Idzuchi, H.; Otani, Y.; Kondou, K.; Fukuma, Y.

    2015-09-21

    We have studied spin relaxation characteristics in a Ag nanowire covered with various oxide layers of Bi{sub 2}O{sub 3}, Al{sub 2}O{sub 3}, HfO{sub 2}, MgO, or AgO{sub x} by using non-local spin valve structures. The spin-flip probability, a ratio of momentum relaxation time to spin relaxation time at 10 K, exhibits a gradual increase with an atomic number of the oxide constituent elements, Mg, Al, Ag, and Hf. Surprisingly, the Bi{sub 2}O{sub 3} capping was found to increase the probability by an order of magnitude compared with other oxide layers. This finding suggests the presence of an additional spin relaxation mechanism such as Rashba effect at the Ag/Bi{sub 2}O{sub 3} interface, which cannot be explained by the simple Elliott-Yafet mechanism via phonon, impurity, and surface scatterings. The Ag/Bi{sub 2}O{sub 3} interface may provide functionality as a spin to charge interconversion layer.

  12. Paramagnetic Inversion of the Sign of the Interference Contribution to the Transverse Relaxation of the Imido Protons of the Coordinated Imidazoles in the Uniformly 15N-Labeled Cytochrome c3

    NASA Astrophysics Data System (ADS)

    Ohmura, Tomoaki; Harada, Erisa; Fujiwara, Toshimichi; Kawai, Gota; Watanabe, Kimitsuna; Akutsu, Hideo

    1998-04-01

    In the spectrum of uniformly15N-labeled cytochromec3, the relative linewidths of the doublet peaks of the15N-coupled imido proton of the coordinated imidazole group were reversed on oxidation. This inversion was explained by the interference relaxation process between the electron-proton dipolar and15N-1H dipolar interactions. The inversion can be used to assign the imido protons of the coordinated imidazole groups in heme proteins.

  13. Suppression of Spin-Exchange Relaxation Using Pulsed Parametric Resonance

    NASA Astrophysics Data System (ADS)

    Korver, A.; Wyllie, R.; Lancor, B.; Walker, T. G.

    2013-07-01

    We demonstrate that spin-exchange dephasing of Larmor precession at near-Earth-scale fields is effectively eliminated by dressing the alkali-metal atom spins in a sequence of ac-coupled 2π pulses, repeated at the Larmor precession frequency. The contribution of spin-exchange collisions to the spectroscopic linewidth is reduced by a factor of the duty cycle of the pulses. We experimentally demonstrate resonant transverse pumping in magnetic fields as high as 0.1 G, present experimental measurements of the suppressed spin-exchange relaxation, and show enhanced magnetometer response relative to a light-narrowed scalar magnetometer.

  14. The Elliott-Yafet theory of spin relaxation generalized for large spin-orbit coupling

    PubMed Central

    Kiss, Annamária; Szolnoki, Lénard; Simon, Ferenc

    2016-01-01

    We generalize the Elliott-Yafet (EY) theory of spin relaxation in metals with inversion symmetry for the case of large spin-orbit coupling (SOC). The EY theory treats the SOC to the lowest order but this approach breaks down for metals of heavy elements (such as e.g. caesium or gold), where the SOC energy is comparable to the relevant band-band separation energies. The generalized theory is presented for a four-band model system without band dispersion, where analytic formulae are attainable for arbitrary SOC for the relation between the momentum- and spin-relaxation rates. As an extended description, we also consider an empirical pseudopotential approximation where SOC is deduced from the band potential (apart from an empirical scaling constant) and the spin-relaxation rate can be obtained numerically. Both approaches recover the usual EY theory for weak SOC and give that the spin-relaxation rate approaches the momentum-relaxation rate in the limit of strong SOC. We argue that this limit is realized in gold by analyzing spin relaxation data. A calculation of the g-factor shows that the empirical Elliott-relation, which links the g-factor and spin-relaxation rate, is retained even for strong SOC. PMID:26943483

  15. The Elliott-Yafet theory of spin relaxation generalized for large spin-orbit coupling.

    PubMed

    Kiss, Annamária; Szolnoki, Lénard; Simon, Ferenc

    2016-01-01

    We generalize the Elliott-Yafet (EY) theory of spin relaxation in metals with inversion symmetry for the case of large spin-orbit coupling (SOC). The EY theory treats the SOC to the lowest order but this approach breaks down for metals of heavy elements (such as e.g. caesium or gold), where the SOC energy is comparable to the relevant band-band separation energies. The generalized theory is presented for a four-band model system without band dispersion, where analytic formulae are attainable for arbitrary SOC for the relation between the momentum- and spin-relaxation rates. As an extended description, we also consider an empirical pseudopotential approximation where SOC is deduced from the band potential (apart from an empirical scaling constant) and the spin-relaxation rate can be obtained numerically. Both approaches recover the usual EY theory for weak SOC and give that the spin-relaxation rate approaches the momentum-relaxation rate in the limit of strong SOC. We argue that this limit is realized in gold by analyzing spin relaxation data. A calculation of the g-factor shows that the empirical Elliott-relation, which links the g-factor and spin-relaxation rate, is retained even for strong SOC. PMID:26943483

  16. Large spin relaxation rates in trapped submerged-shell atoms

    SciTech Connect

    Connolly, Colin B.; Au, Yat Shan; Doret, S. Charles; Doyle, John M.; Ketterle, Wolfgang

    2010-01-15

    Spin relaxation due to atom-atom collisions is measured for magnetically trapped erbium and thulium atoms at a temperature near 500 mK. The rate constants for Er-Er and Tm-Tm collisions are 3.0x10{sup -10} and 1.1x10{sup -10} cm{sup 3} s{sup -1}, respectively, 2-3 orders of magnitude larger than those observed for highly magnetic S-state atoms. This is strong evidence for an additional, dominant, spin relaxation mechanism, electronic interaction anisotropy, in collisions between these 'submerged-shell,' Lnot =0 atoms. These large spin relaxation rates imply that evaporative cooling of these atoms in a magnetic trap will be highly inefficient.

  17. Synthesis of 14N and 15N-labeled trityl-nitroxide biradicals with strong spin-spin interaction and improved sensitivity to redox status and oxygen

    PubMed Central

    Liu, Yangping; Villamena, Frederick A.; Song, Yuguang; Sun, Jian; Rockenbauer, Antal

    2014-01-01

    Simultaneous evaluation redox status and oxygenation in biological systems is of great importance for the understanding of biological functions. Electron paramagnetic resonance spectroscopy coupled with the use of the nitroxide radicals have been an indispensable technique for this application but are still limited by its low oxygen sensitivity, and low EPR resolution in part due to the moderately broad EPR triplet and spin quenching through bioreduction. In this study, we showed that these drawbacks can be overcome through the use of trityl-nitroxide biradicals allowing for the simultaneous measurement of redox status and oxygenation. A new trityl-nitroxide biradical TNN14 composed of a pyrrolidinyl-nitroxide and a trityl, and its isotopically labeled 15N analogue TNN15 were synthesized and characterized. Both biradicals exhibited much stronger spin-spin interaction with J > 400 G than the previous synthesized trityl-nitroxide biradicals TN1 (~160 G) and TN2 (~52 G) with longer linker chain length. The enhanced stability of TNN14 was evaluated using ascorbate as reductant and the effect of different types of cyclodextrins on its stability in the presence of ascorbate was also investigated. Both biradicals are sensitive to redox status, and their corresponding trityl-hydroxylamines resulting from the reduction of the biradicals by ascorbate share the same oxygen sensitivity. Of note is that the 15N-labeled TNN15-H with an EPR doublet exhibits improved EPR signal amplitude as compared to TNN14-H with an EPR triplet. In addition, cyclic voltammetric studies verify the characteristic electrochemical behaviors of the trityl-nitroxide biradicals. PMID:21028905

  18. H/D exchange of a 15N labelled Tau fragment as measured by a simple Relax-EXSY experiment

    NASA Astrophysics Data System (ADS)

    Lopez, Juan; Ahuja, Puneet; Landrieu, Isabelle; Cantrelle, François-Xavier; Huvent, Isabelle; Lippens, Guy

    2014-12-01

    We present an equilibrium H/D exchange experiment to measure the exchange rates of labile amide protons in intrinsically unfolded proteins. By measuring the contribution of the H/D exchange to the apparent T1 relaxation rates in solvents of different D2O content, we can easily derive the rates of exchange for rapidly exchanging amide protons. The method does not require double isotope labelling, is sensitive, and requires limited fitting of the data. We demonstrate it on a functional fragment of Tau, and provide evidence for the hydrogen bond formation of the phosphate moiety of Ser214 with its own amide proton in the same fragment phosphorylated by the PKA kinase.

  19. Direct and cost-efficient hyperpolarization of long-lived nuclear spin states on universal 15N2-diazirine molecular tags

    PubMed Central

    Theis, Thomas; Ortiz, Gerardo X.; Logan, Angus W. J.; Claytor, Kevin E.; Feng, Yesu; Huhn, William P.; Blum, Volker; Malcolmson, Steven J.; Chekmenev, Eduard Y.; Wang, Qiu; Warren, Warren S.

    2016-01-01

    Conventional magnetic resonance (MR) faces serious sensitivity limitations which can be overcome by hyperpolarization methods, but the most common method (dynamic nuclear polarization) is complex and expensive, and applications are limited by short spin lifetimes (typically seconds) of biologically relevant molecules. We use a recently developed method, SABRE-SHEATH, to directly hyperpolarize 15N2 magnetization and long-lived 15N2 singlet spin order, with signal decay time constants of 5.8 and 23 minutes, respectively. We find >10,000-fold enhancements generating detectable nuclear MR signals that last for over an hour. 15N2-diazirines represent a class of particularly promising and versatile molecular tags, and can be incorporated into a wide range of biomolecules without significantly altering molecular function. PMID:27051867

  20. Analysis of internal motions of interleukin-13 variant associated with severe bronchial asthma using {sup 15}N NMR relaxation measurements

    SciTech Connect

    Yoshida, Yuichiro; Ohkuri, Takatoshi; Takeda, Chika; Kuroki, Ryota; Izuhara, Kenji; Imoto, Taiji; Ueda, Tadashi . E-mail: ueda@phar.kyushu-u.ac.jp

    2007-06-22

    The single nucleotide polymorphism interleukin-13 (IL-13) R110Q is associated with severe bronchial asthma because its lower affinity leads to the augmentation of local IL-13 concentration, resulting in an increase in the signal transduction via IL-13R. Since the mutation site does not directly bind to IL-13R{alpha}2, we carried out NMR relaxation analyses of the wild-type IL-13 and IL-13-R110Q in order to examine whether the R110Q mutation affects the internal motions in IL-13 molecules. The results showed that the internal motion in the micro- to millisecond time scale on helix D, which is suggested to be important for the interaction between IL-13 and IL-13R{alpha}2, is increased in IL-13-R110Q compared with that in the wild-type IL-13. It therefore appears that the difference in the internal motions on helix D between the wild-type IL-13 and IL-13-R110Q may be involved in their affinity differences with IL-13R{alpha}2.

  1. Mechanisms of relaxation and spin decoherence in nanomagnets

    NASA Astrophysics Data System (ADS)

    van Tol, Johan

    Relaxation in spin systems is of great interest with respect to various possible applications like quantum information processing and storage, spintronics, and dynamic nuclear polarization (DNP). The implementation of high frequencies and fields is crucial in the study of systems with large zero-field splitting or large interactions, as for example molecular magnets and low dimensional magnetic materials. Here we will focus on the implementation of pulsed Electron Paramagnetic Resonance (ERP) at multiple frequencies of 10, 95, 120, 240, and 336 GHz, and the relaxation and decoherence processes as a function of magnetic field and temperature. Firstly, at higher frequencies the direct single-phonon spin-lattice relaxation (SLR) is considerably enhanced, and will more often than not be the dominant relaxation mechanism at low temperatures, and can be much faster than at lower fields and frequencies. In principle the measurement of the SLR rates as a function of the frequency provides a means to map the phonon density of states. Secondly, the high electron spin polarization at high fields has a strong influence on the spin fluctuations in relatively concentrated spin systems, and the contribution of the electron-electron dipolar interactions to the coherence rate can be partially quenched at low temperatures. This not only allows the study of relatively concentrated spin systems by pulsed EPR (as for example magnetic nanoparticles and molecular magnets), it enables the separation of the contribution of the fluctuations of the electron spin system from other decoherence mechanisms. Besides choice of temperature and field, several strategies in sample design, pulse sequences, or clock transitions can be employed to extend the coherence time in nanomagnets. A review will be given of the decoherence mechanisms with an attempt at a quantitative comparison of experimental rates with theory.

  2. Spin dynamics simulation of electron spin relaxation in Ni{sup 2+}(aq)

    SciTech Connect

    Rantaharju, Jyrki Mareš, Jiří Vaara, Juha

    2014-07-07

    The ability to quantitatively predict and analyze the rate of electron spin relaxation of open-shell systems is important for electron paramagnetic resonance and paramagnetic nuclear magnetic resonance spectroscopies. We present a combined molecular dynamics (MD), quantum chemistry (QC), and spin dynamics simulation method for calculating such spin relaxation rates. The method is based on the sampling of a MD trajectory by QC calculations, to produce instantaneous parameters of the spin Hamiltonian used, in turn, to numerically solve the Liouville-von Neumann equation for the time evolution of the spin density matrix. We demonstrate the approach by simulating the relaxation of electron spin in an aqueous solution of Ni{sup 2+} ion. The spin-lattice (T{sub 1}) and spin-spin (T{sub 2}) relaxation rates are extracted directly from the simulations of the time dependence of the longitudinal and transverse magnetization, respectively. Good agreement with the available, indirectly obtained experimental data is obtained by our method.

  3. NMR spin relaxation rates in the Heisenberg bilayer

    NASA Astrophysics Data System (ADS)

    Mendes, Tiago; Curro, Nicholas; Scalettar, Richard; Paiva, Thereza; Dos Santos, Raimundo R.

    One of the striking features of heavy fermions is the fact that in the vicinity of a quantum phase transition these systems exhibit the breakdown of Fermi-liquid behavior and superconductivity. Nuclear magnetic resonance (NMR) expirements play an important role in the study of these phenomena. Measurements of NMR spin relaxation rates and Knight shift, for instance, can be used to probe the electronic spin susceptibility of these systems. Here we studied the NMR response of the Heisenberg bilayer model. In this model, it is well known that the increase of the interplane coupling between the planes, Jperp, supresses the antiferromagnetic order at a quantum critical point (QCP). We use stochastic series expansion (SSE) and the maximum-entropy analytic continuation method to calculate the NMR spin lattice relaxation rate 1 /T1 and the spin echo decay 1 /T2 G as function of Jperp. The spin echo decay, T2 G increases for small Jperp, due to the increase of the order parameter, and then vanishes abruptly in the QCP. The effects of Jperp dilution disorder in the QCP and the relaxation rates are also discussed. This research was supported by the NNSA Grant Number DE-NA 0002908, and Ciência sem fronteiras program/CNPQ.

  4. Spin-exchange-relaxation-free magnetometry with Cs vapor

    NASA Astrophysics Data System (ADS)

    Ledbetter, M. P.; Savukov, I. M.; Acosta, V. M.; Budker, D.; Romalis, M. V.

    2008-03-01

    We describe a Cs atomic magnetometer operating in the spin-exchange-relaxation-free (SERF) regime. With a vapor cell temperature of 103°C we achieve intrinsic magnetic resonance widths ΔB=17μG corresponding to an electron spin-relaxation rate of 300s-1 when the spin-exchange rate is ΓSE=14000s-1 . We also observe an interesting narrowing effect due to diffusion. Signal-to-noise measurements yield a sensitivity of about 400pG/Hz . Based on photon shot noise, we project a sensitivity of 40pG/Hz . A theoretical optimization of the magnetometer indicates sensitivities on the order of 2pG/Hz should be achievable in a 1cm3 volume. Because Cs has a higher saturated vapor pressure than other alkali metals, SERF magnetometers using Cs atoms are particularly attractive in applications requiring lower temperatures.

  5. Nuclear spin relaxation in ordered bimetallic chain compounds

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shoji

    2000-01-01

    A theoretical interpretation is given to recent proton spin relaxation-time ( T1) measurements on NiCu(C 7H 6N 2O 6)(H 2O) 3·2H 2O, which is an ideal one-dimensional ferrimagnetic Heisenberg model system of alternating spins 1 and {1}/{2}. The relaxation rate T1-1 is formulated in terms of the spin-wave theory and is evaluated by the use of a quantum Monte Carlo method. Calculations of the temperature and applied-field ( H) dependences of T1-1 are in total agreement with the experimental findings. T1 behaves as T1-1∝ H-1/2, which turns out an indirect observation of the quadratic dispersion relations dominating the low-energy physics of quantum ferrimagnets.

  6. Spin relaxation in n-type GaAs quantum wells with transient spin grating

    NASA Astrophysics Data System (ADS)

    Weng, M. Q.; Wu, M. W.; Cui, H. L.

    2008-03-01

    By solving the kinetic spin Bloch equations, we study the time evolution of the transient spin grating, whose spin polarization periodically varies in real space, confined in (001) GaAs quantum wells. With this study, we can investigate the properties of both the spin transport and the spin relaxation at the same time. The Fourier component of the spin signal double exponentially decays with two decay rates 1/τ+ and 1/τ-. In the high temperature regime, the average of these two rates quadratically varies with the grating wave vector q, i.e., (1/τ++1/τ-)/2=Dsq2+1/τ˜s, with Ds and τ˜s representing the spin diffusion coefficient and the average of the out-of-plane and the in-plane spin relaxation times, respectively. τ± calculated from our theory are in good agreement with the experimental data by Weber et al. [Phys. Rev. Lett. 98, 076604 (2007)]. By comparing Ds with and without the electron-electron Coulomb scattering, we calculate the contribution of Coulomb drag to the spin diffusion coefficient. With the transient spin grating result, we further reveal the relations among different characteristic parameters such as spin diffusion coefficient Ds, spin relaxation time τs, and spin injection length Ls. We show that in the presence of the Dresselhaus and/or Rashba spin-orbit coupling, the widely used relation Ls=√Dsτs is generally inaccurate and can even be very wrong in some special cases. We present an accurate way to extract the steady-state transport characteristic parameters from the transient spin grating signals.

  7. Muon spin relaxation studies of interstitial and molecular motion.

    PubMed

    Cox, S F

    1998-03-01

    The unusual methods of preparation and analysis of spin polarization in muSR spectroscopy, which exploit the unique properties of the positive muon, are introduced in this article. Following a summary overview of applications, particular attention is paid to the problem of spin-lattice relaxation for a muon experiencing a hyperfine interaction with a single unpaired electron. The specific cases considered are the interstitial diffusion of muonium--the 1-electron atom which may be considered as a light isotope of hydrogen-and the molecular dynamics of organic radicals labelled by muonium. Rate equations for the evolution of population in the hyperfine-coupled spin states are solved numerically for various relaxation mechanisms. The formalism is equally valid for conventional ESR studies of paramagnetic states but is pursued specifically to simulate T1-relaxation in muSR. The simulations are compared with literature data. Also treated is the case of intermittent hyperfine coupling, appropriate to electron capture and loss in semiconductors or soliton motion in polymers; for this, a Monte Carlo approach is used to simulate the muon response. (For low-dimensional motion, the relaxation function is not exponential, so that a unique value of T1 cannot be defined.) Finally, a proposal is made to implement muon-T1 measurements in the rotating frame; this is designed for the selective study of electronically diamagnetic muonium states (i.e., those without hyperfine coupling) in the presence of a paramagnetic muonium or radical fraction.

  8. Muon spin relaxation studies of interstitial and molecular motion.

    PubMed

    Cox, S F

    1998-03-01

    The unusual methods of preparation and analysis of spin polarization in muSR spectroscopy, which exploit the unique properties of the positive muon, are introduced in this article. Following a summary overview of applications, particular attention is paid to the problem of spin-lattice relaxation for a muon experiencing a hyperfine interaction with a single unpaired electron. The specific cases considered are the interstitial diffusion of muonium--the 1-electron atom which may be considered as a light isotope of hydrogen-and the molecular dynamics of organic radicals labelled by muonium. Rate equations for the evolution of population in the hyperfine-coupled spin states are solved numerically for various relaxation mechanisms. The formalism is equally valid for conventional ESR studies of paramagnetic states but is pursued specifically to simulate T1-relaxation in muSR. The simulations are compared with literature data. Also treated is the case of intermittent hyperfine coupling, appropriate to electron capture and loss in semiconductors or soliton motion in polymers; for this, a Monte Carlo approach is used to simulate the muon response. (For low-dimensional motion, the relaxation function is not exponential, so that a unique value of T1 cannot be defined.) Finally, a proposal is made to implement muon-T1 measurements in the rotating frame; this is designed for the selective study of electronically diamagnetic muonium states (i.e., those without hyperfine coupling) in the presence of a paramagnetic muonium or radical fraction. PMID:9650794

  9. Mechanisms of Gadographene-Mediated Proton Spin Relaxation

    PubMed Central

    Hung, Andy H.; Duch, Matthew C.; Parigi, Giacomo; Rotz, Matthew W.; Manus, Lisa M.; Mastarone, Daniel J.; Dam, Kevin T.; Gits, Colton C.; MacRenaris, Keith W.; Luchinat, Claudio; Hersam, Mark C.; Meade, Thomas J.

    2013-01-01

    Gd(III) associated with carbon nanomaterials relaxes water proton spins at an effectiveness that approaches or exceeds the theoretical limit for a single bound water molecule. These Gd(III)-labeled materials represent a potential breakthrough in sensitivity for Gd(III)-based contrast agents used for magnetic resonance imaging (MRI). However, their mechanism of action remains unclear. A gadographene library encompassing GdCl3, two different Gd(III)-complexes, graphene oxide (GO), and graphene suspended by two different surfactants and subjected to varying degrees of sonication was prepared and characterized for their relaxometric properties. Gadographene was found to perform comparably to other Gd(III)-carbon nanomaterials; its longitudinal (r1) and transverse (r2) relaxivity is modulated between 12–85 mM−1s−1 and 24–115 mM−1s−1, respectively, depending on the Gd(III)-carbon backbone combination. The unusually large relaxivity and its variance can be understood under the modified Florence model incorporating the Lipari-Szabo approach. Changes in hydration number (q), water residence time (τM), molecular tumbling rate (τR), and local motion (τfast) sufficiently explain most of the measured relaxivities. Furthermore, results implicated the coupling between graphene and Gd(III) as a minor contributor to proton spin relaxation. PMID:24298299

  10. Spin Relaxation in Hyperpolarized He-3 Fermi Liquids

    NASA Astrophysics Data System (ADS)

    Stanton, Liam; Bedell, Kevin

    2004-03-01

    In the past few years, attention has been drawn towards the hyperpolarized gases of Xenon-129 and Helium-3 isotopes. Medical research has explored the possibilities of using these isotopes for magnetic resonance imaging (MRI) of the lungs in both human and animal test subjects. Because the atoms of hyperpolarized gas are forced into a specific spin state, the MRI signal is enhanced. While the spin relaxation times of Helium-3 can be calculated in the high and low temperature limits, there exists no exact analytic solution for intermediate temperatures. The intention of this research was to numerically connect these limits with an accurate approximation. To do this, various analytic and numerical methods were used to reduce the spin relaxation time to a function of temperature, chemical potential, and particle number. Additional numerical methods were then used to calculate the chemical potential of Helium-3. The data show that a minimum occurs in the spin relaxation time at the order of the Fermi temperature, after which the classical limit is rapidly approached. These computational results seem to coincide with those expected.

  11. General theoretical/computational tool for interpreting NMR spin relaxation in proteins.

    PubMed

    Zerbetto, Mirco; Polimeno, Antonino; Meirovitch, Eva

    2009-10-15

    We developed in recent years the slowly relaxing local structure (SRLS) approach for analyzing NMR spin relaxation in proteins. SRLS is a two-body coupled rotator model which accounts rigorously for mode-coupling between the global motion of the protein and the local motion of the spin-bearing probe and allows for general properties of the second rank tensors involved. We showed that a general tool of data analysis requires both capabilities. Several important functionalities were missing in our previous implementations of SRLS in data fitting schemes, and in some important cases, the calculations were tedious. Here we present a general implementation which allows for asymmetric local and global diffusion tensors, distinct local ordering and local diffusion frames, and features a rhombic local potential which includes Wigner matrix element terms of ranks 2 and 4. A recently developed hydrodynamics-based approach for calculating global diffusion tensors has been incorporated into the data-fitting scheme. The computational efficiency of the latter has been increased significantly through object-oriented programming within the scope of the C++ programming language, and code parallelization. A convenient graphical user interface is provided. Currently autocorrelated (15)N spin relaxation data can be analyzed effectively. Adaptation to any autocorrelated and cross-correlated relaxation analysis is straightforward. New physical insight is gleaned on largely preserved local structure in solution, even in chain segments which experience slow local motion. Prospects associated with improved dynamic models, and new applications made possible by the current implementation of SRLS, are delineated. PMID:19775101

  12. Direct observation of thermal relaxation in artificial spin ice.

    PubMed

    Farhan, A; Derlet, P M; Kleibert, A; Balan, A; Chopdekar, R V; Wyss, M; Perron, J; Scholl, A; Nolting, F; Heyderman, L J

    2013-08-01

    We study the thermal relaxation of artificial spin ice with photoemission electron microscopy, and are able to directly observe how such a system finds its way from an energetically excited state to the ground state. On plotting vertex-type populations as a function of time, we can characterize the relaxation, which occurs in two stages, namely a string and a domain regime. Kinetic Monte Carlo simulations agree well with the temporal evolution of the magnetic state when including disorder, and the experimental results can be explained by considering the effective interaction energy associated with the separation of pairs of vertex excitations. PMID:23952441

  13. Electron number dependence of spin triplet-singlet relaxation time

    NASA Astrophysics Data System (ADS)

    Li, H. O.; Xiao, M.; Cao, G.; You, J.; Guo, G. P.

    2014-02-01

    In a GaAs single quantum dot, the relaxation time T1 between spin triplet and singlet states has been measured for the last few even electron numbers. The singlet-triplet energy separation EST is tuned as a control parameter for the comparison of T1 between different electron numbers. T1 steadily decreases with increasing electron numbers from 2-electrons to 6-electrons. This implies an enhancement of the spin-orbit coupling strength due to multi-electron interaction in a quantum dot.

  14. Hyperpolarized nanodiamond with long spin-relaxation times

    PubMed Central

    Rej, Ewa; Gaebel, Torsten; Boele, Thomas; Waddington, David E.J.; Reilly, David J.

    2015-01-01

    The use of hyperpolarized agents in magnetic resonance, such as 13C-labelled compounds, enables powerful new imaging and detection modalities that stem from a 10,000-fold boost in signal. A major challenge for the future of the hyperpolarization technique is the inherently short spin-relaxation times, typically <60 s for 13C liquid-state compounds, which limit the time that the signal remains boosted. Here we demonstrate that 1.1% natural abundance 13C spins in synthetic nanodiamond can be hyperpolarized at cryogenic and room temperature without the use of free radicals, and, owing to their solid-state environment, exhibit relaxation times exceeding 1 h. Combined with the already established applications of nanodiamonds in the life sciences as inexpensive fluorescent markers and non-cytotoxic substrates for gene and drug delivery, these results extend the theranostic capabilities of nanoscale diamonds into the domain of hyperpolarized magnetic resonance. PMID:26450570

  15. Kinetic theories for spin models for cooperative relaxation dynamics

    NASA Astrophysics Data System (ADS)

    Pitts, Steven Jerome

    The facilitated kinetic Ising models with asymmetric spin flip constraints introduced by Jackle and co-workers [J. Jackle, S. Eisinger, Z. Phys. B 84, 115 (1991); J. Reiter, F. Mauch, J. Jackle, Physica A 184, 458 (1992)] exhibit complex relaxation behavior in their associated spin density time correlation functions. This includes the growth of relaxation times over many orders of magnitude when the thermodynamic control parameter is varied, and, in some cases, ergodic-nonergodic transitions. Relaxation equations for the time dependence of the spin density autocorrelation function for a set of these models are developed that relate this autocorrelation function to the irreducible memory function of Kawasaki [K. Kawasaki, Physica A 215, 61 (1995)] using a novel diagrammatic series approach. It is shown that the irreducible memory function in a theory of the relaxation of an autocorrelation function in a Markov model with detailed balance plays the same role as the part of the memory function approximated by a polynomial function of the autocorrelation function with positive coefficients in schematic simple mode coupling theories for supercooled liquids [W. Gotze, in Liquids, Freezing and the Glass Transition, D. Levesque, J. P. Hansen, J. Zinn-Justin eds., 287 (North Holland, New York, 1991)]. Sets of diagrams in the series for the irreducible memory function are summed which lead to approximations of this type. The behavior of these approximations is compared with known results from previous analytical calculations and from numerical simulations. For the simplest one dimensional model, relaxation equations that are closely related to schematic extended mode coupling theories [W. Gotze, ibid] are also derived using the diagrammatic series. Comparison of the results of these approximate theories with simulation data shows that these theories improve significantly on the results of the theories of the simple schematic mode coupling theory type. The potential

  16. Search for exotic spin-dependent interactions with a spin-exchange relaxation-free magnetometer

    NASA Astrophysics Data System (ADS)

    Chu, P.-H.; Kim, Y. J.; Savukov, I.

    2016-08-01

    We propose a novel experimental approach to explore exotic spin-dependent interactions using a spin-exchange relaxation-free (SERF) magnetometer, the most sensitive noncryogenic magnetic-field sensor. This approach studies the interactions between optically polarized electron spins located inside a vapor cell of the SERF magnetometer and unpolarized or polarized particles of external solid-state objects. The coupling of spin-dependent interactions to the polarized electron spins of the magnetometer induces the tilt of the electron spins, which can be detected with high sensitivity by a probe laser beam similarly as an external magnetic field. We estimate that by moving unpolarized or polarized objects next to the SERF Rb vapor cell, the experimental limit to the spin-dependent interactions can be significantly improved over existing experiments, and new limits on the coupling strengths can be set in the interaction range below 10-2 m .

  17. Spin-flip relaxation via optical phonon scattering in quantum dots

    SciTech Connect

    Wang, Zi-Wu; Liu, Lei; Li, Shu-Shen

    2013-12-14

    Based on the spin-orbit coupling admixture mechanism, we theoretically investigate the spin-flip relaxation via optical phonon scattering in quantum dots by considering the effect of lattice relaxation due to the electron-acoustic phonon deformation potential coupling. The relaxation rate displays a cusp-like structure (or a spin hot spot) that becomes more clearly with increasing temperature. We also calculate the relaxation rate of the spin-conserving process, which follows a Gaussian form and is several orders of magnitude larger than that of spin-flip process. Moreover, we find that the relaxation rate displays the oscillatory behavior due to the interplay effects between the magnetic and spatial confinement for the spin-flip process not for the spin-conserving process. The trends of increasing and decreasing temperature dependence of the relaxation rates for two relaxation processes are obtained in the present model.

  18. Possible spin frustration in Nd2Ti2O7 probed by muon spin relaxation.

    PubMed

    Guo, Hanjie; Xing, Hui; Tong, Jun; Tao, Qian; Watanabe, Isao; Xu, Zhu-an

    2014-10-29

    Muon spin relaxation on Nd2Ti2O7 (NTO) and NdLaTi2O7 (NLTO) compounds are presented. The time spectra for both compounds are as expected for the paramagnetic state at high temperatures, but deviate from the exponential function below around 100 K. Firstly, the muon spin relaxation rate increases with decreasing temperature and then levels off below around 10 K, which is reminiscent of the frustrated systems. An enhancement of the relaxation rate by a longitudinal field in the paramagnetic state is observed for NTO and eliminated by a magnetic dilution for the NLTO sample. This suggests that the spectral density is modified by a magnetic dilution and thus indicates that the spins behave cooperatively rather than individually. The zero-field measurement at 0.3 K indicates that the magnetic ground state for NTO is ferromagnetic.

  19. Spin Relaxation in Spherical CdS Quantum Dots

    NASA Astrophysics Data System (ADS)

    Nahalkova, P.; Sprinzl, D.; Nemec, P.; Maly, P.; Gladilin, V. N.; Devreese, J. T.

    2006-03-01

    We present results of the time-resolved spin-sensitive differential transmission experiments and the quantitative theoretical analysis of the spin relaxation mechanism in quasi-spherical CdS quantum dots (QD) in a glass matrix. The measured decay of the degree of circular polarization (DCP) on ns timescale can be explained well by intralevel exciton transitions with electron spin flip, driven by the electron-hole exchange interaction and assisted by two LO phonons. The predicted spin relaxation rates for different QD sizes and temperatures are in line with experimentally determined values. The developed theoretical model provides also a qualitative understanding of the observed behavior of DCP as a function of central energy of pump and probe pulses. This work was supported by the Ministry of Education of the Czech Republic in the framework of research plan MSM 0021620834 and the research centre LC510, as well as by the GOA BOF UA 2000, IUAP, FWO-V projects G.0274.01N, G.0435.03, WOG WO.035.04N (Belgium) and the European Commission SANDiE Network of Excellence, contract No. NMP4-CT-2004-500101.

  20. Influence of subdiffusive motion on spin relaxation and spin effects in radical pairs.

    PubMed

    Shushin, A I

    2006-02-23

    Specific features of spin relaxation and the kinetics of spin effect generation in radical pairs (RPs) undergoing subdiffusive relative motion are studied in detail. Two types of processes are analyzed: (1) spin relaxation in biradicals, resulting from anomalously slow subdiffuisive reorientation (with the correlation function P(t) approximately (wt)(-alpha), where 0 < alpha < 1) and (2) spin effect generation in subdiffusion-assisted RP recombination. Analysis is made with the use of the non-Markovian stochastic Liouville equation (SLE) derived within the continuous time random walk approach. The SLE predicts anomalous (very slow and nonexponential) spin relaxation in biradicals which results in some peculiarities of the spectrum of the system. In RP recombination, the subdiffusive relative motion shows itself in slow dependence of the reaction yield Y(r)() on reactivity and parameters of the RP spin Hamiltonian and anomalous electron spin polarization of escaped radicals. The spectrum of the reaction yield detected magnetic resonance, that is, the Y(r)() dependence on the frequency omega of microwave field, is found to be strongly non-Lorenzian with the width determined by the field strength omega(1) and very broad wings depending on alpha. Analysis shows that the majority of interesting, specific features of the observables in both systems are controlled only by the parameter alpha.

  1. The spin-temperature theory of dynamic nuclear polarization and nuclear spin-lattice relaxation

    NASA Technical Reports Server (NTRS)

    Byvik, C. E.; Wollan, D. S.

    1974-01-01

    A detailed derivation of the equations governing dynamic nuclear polarization (DNP) and nuclear spin lattice relaxation by use of the spin temperature theory has been carried to second order in a perturbation expansion of the density matrix. Nuclear spin diffusion in the rapid diffusion limit and the effects of the coupling of the electron dipole-dipole reservoir (EDDR) with the nuclear spins are incorporated. The complete expression for the dynamic nuclear polarization has been derived and then examined in detail for the limit of well resolved solid effect transitions. Exactly at the solid effect transition peaks, the conventional solid-effect DNP results are obtained, but with EDDR effects on the nuclear relaxation and DNP leakage factor included. Explicit EDDR contributions to DNP are discussed, and a new DNP effect is predicted.

  2. Nonlinear effects in spin relaxation of cavity polaritons

    SciTech Connect

    Solnyshkov, D. D.; Shelykh, I. A. Glazov, M. M.; Malpuech, G.; Amand, T.; Renucci, P.; Marie, X.; Kavokin, A. V.

    2007-09-15

    We present the general kinetic formalism for the description of spin and energy relaxation of the cavity polaritons in the framework of the Born-Markov approximation. All essential mechanisms of polariton redistribution in reciprocal space together with the final state bosonic stimulation are taken into account from our point of view. The developed theory is applied to describe our experimental results on the polarization dynamics obtained in the polariton parametric amplifier geometry (pumping at the so-called magic angle). Under circular pumping, we show that the spin relaxation time is strongly dependent on the detuning between the exciton and cavity mode energies mainly because of the influence of the detuning on the coupling strength between the photon-like part of the exciton-polariton lower dispersion branch and the reservoir of uncoupled exciton states. In the negative detuning case we find a very long spin relaxation time of about 300 ps. In the case of excitation by a linearly polarized light, we have experimentally confirmed that the anisotropy of the polariton-polariton interaction is responsible for the build-up of the cross-linear polarization of the signal. In the spontaneous regime the polarization degree of the signal is -8% but it can reach -65% in the stimulated regime. The long-living linear polarization observed at zero detuning indicates that the reservoir is formed by excitons localized at the anisotropic islands oriented along the crystallographic axes. Finally, under elliptical pumping, we have directly measured in the time domain and modeled the effect of self-induced Larmor precession, i.e., the rotation of the linear polarization of a state about an effective magnetic field proportional to the projection of the total spin of exciton-polaritons in the cavity on its growth axis.

  3. Spin-orbit induced two-electron spin relaxation in double quantum dots

    NASA Astrophysics Data System (ADS)

    Borhani, Massoud; Hu, Xuedong

    2011-03-01

    We study the spin decay of two electrons confined in a double quantum dots via the spin-orbit interaction and acoustic phonons. We have obtained a generic form for the spin Hamiltonian for two electrons confined in (elliptic) harmonic potentials in doubles dots and in the presence of an arbitrary applied magnetic field. Our focus is on the interdot bias regime where singlet-triplet splitting is small, in contrast to the spin-blockade regime. Our results clarify the spin-orbit mediated two-spin relaxation in lateral/nanowire quantum dots, particularly when the confining potentials are different in each dot. We thank support by NSA/LPS thorugh ARO.

  4. Cross-Correlated Relaxation of Dipolar Coupling and Chemical-Shift Anisotropy in Magic-Angle Spinning R1ρ NMR Measurements: Application to Protein Backbone Dynamics Measurements.

    PubMed

    Kurauskas, Vilius; Weber, Emmanuelle; Hessel, Audrey; Ayala, Isabel; Marion, Dominique; Schanda, Paul

    2016-09-01

    Transverse relaxation rate measurements in magic-angle spinning solid-state nuclear magnetic resonance provide information about molecular motions occurring on nanosecond-to-millisecond (ns-ms) time scales. The measurement of heteronuclear ((13)C, (15)N) relaxation rate constants in the presence of a spin-lock radiofrequency field (R1ρ relaxation) provides access to such motions, and an increasing number of studies involving R1ρ relaxation in proteins have been reported. However, two factors that influence the observed relaxation rate constants have so far been neglected, namely, (1) the role of CSA/dipolar cross-correlated relaxation (CCR) and (2) the impact of fast proton spin flips (i.e., proton spin diffusion and relaxation). We show that CSA/D CCR in R1ρ experiments is measurable and that the CCR rate constant depends on ns-ms motions; it can thus provide insight into dynamics. We find that proton spin diffusion attenuates this CCR due to its decoupling effect on the doublet components. For measurements of dynamics, the use of R1ρ rate constants has practical advantages over the use of CCR rates, and this article reveals factors that have so far been disregarded and which are important for accurate measurements and interpretation. PMID:27500976

  5. Cross-Correlated Relaxation of Dipolar Coupling and Chemical-Shift Anisotropy in Magic-Angle Spinning R1ρ NMR Measurements: Application to Protein Backbone Dynamics Measurements.

    PubMed

    Kurauskas, Vilius; Weber, Emmanuelle; Hessel, Audrey; Ayala, Isabel; Marion, Dominique; Schanda, Paul

    2016-09-01

    Transverse relaxation rate measurements in magic-angle spinning solid-state nuclear magnetic resonance provide information about molecular motions occurring on nanosecond-to-millisecond (ns-ms) time scales. The measurement of heteronuclear ((13)C, (15)N) relaxation rate constants in the presence of a spin-lock radiofrequency field (R1ρ relaxation) provides access to such motions, and an increasing number of studies involving R1ρ relaxation in proteins have been reported. However, two factors that influence the observed relaxation rate constants have so far been neglected, namely, (1) the role of CSA/dipolar cross-correlated relaxation (CCR) and (2) the impact of fast proton spin flips (i.e., proton spin diffusion and relaxation). We show that CSA/D CCR in R1ρ experiments is measurable and that the CCR rate constant depends on ns-ms motions; it can thus provide insight into dynamics. We find that proton spin diffusion attenuates this CCR due to its decoupling effect on the doublet components. For measurements of dynamics, the use of R1ρ rate constants has practical advantages over the use of CCR rates, and this article reveals factors that have so far been disregarded and which are important for accurate measurements and interpretation.

  6. Site-specific protein backbone and side-chain NMR chemical shift and relaxation analysis of human vinexin SH3 domain using a genetically encoded {sup 15}N/{sup 19}F-labeled unnatural amino acid

    SciTech Connect

    Shi, Pan; Xi, Zhaoyong; Wang, Hu; Shi, Chaowei; Xiong, Ying; Tian, Changlin

    2010-11-19

    Research highlights: {yields} Chemical synthesis of {sup 15}N/{sup 19}F-trifluomethyl phenylalanine. {yields} Site-specific incorporation of {sup 15}N/{sup 19}F-trifluomethyl phenylalanine to SH3. {yields} Site-specific backbone and side chain chemical shift and relaxation analysis. {yields} Different internal motions at different sites of SH3 domain upon ligand binding. -- Abstract: SH3 is a ubiquitous domain mediating protein-protein interactions. Recent solution NMR structural studies have shown that a proline-rich peptide is capable of binding to the human vinexin SH3 domain. Here, an orthogonal amber tRNA/tRNA synthetase pair for {sup 15}N/{sup 19}F-trifluoromethyl-phenylalanine ({sup 15}N/{sup 19}F-tfmF) has been applied to achieve site-specific labeling of SH3 at three different sites. One-dimensional solution NMR spectra of backbone amide ({sup 15}N){sup 1}H and side-chain {sup 19}F were obtained for SH3 with three different site-specific labels. Site-specific backbone amide ({sup 15}N){sup 1}H and side-chain {sup 19}F chemical shift and relaxation analysis of SH3 in the absence or presence of a peptide ligand demonstrated different internal motions upon ligand binding at the three different sites. This site-specific NMR analysis might be very useful for studying large-sized proteins or protein complexes.

  7. Nuclear Spin Relaxation Times for Methane-Helium ``Slush'' at 4 MHz using Pulsed NMR

    NASA Astrophysics Data System (ADS)

    Hamida, J. A.; Sullivan, N. S.

    2006-09-01

    We report measurements of the nuclear spin-lattice relaxation times (T1) and spin-spin relaxation times (T2) for small grains of methane suspended in liquid helium (methane-helium "slush") for temperatures 2 Kspin-spin relaxation rate 1/T2 is consistent with internal diffusion as opposed to surface scattering, which has been shown to be dominant for hydrogen-helium "slush". The most interesting feature observed for methane-helium mixtures is the existence of three different time scales for samples aged at 4.2 K. The possible origins of this distribution of relaxation times are discussed.

  8. Relaxation of AB Spin Systems in Stimulated-Echo Spectroscopy

    NASA Astrophysics Data System (ADS)

    Straubinger, Klaus; Schick, Fritz; Lutz, Otto

    1995-12-01

    The behavior of the strongly coupled AB spin system during the STEAM (stimulated echo acquisition mode) sequence was calculated analytically. Relaxation during the TM interval, in which longitudinal magnetization and zero-quantum coherences (ZQCs) occur, was accounted for by following the course of the different density-matrix terms. The result allows one to determine sequence timings to provide high signal intensities or signals resulting from certain coherences. Theoretically calculated spectra can be generated, using an analytical function. Series of proton spectra were recorded from a 0.1maqueous solution of citrate on a 1.5 T whole-body imager at 22°C. Spectra series with constant echo time TE were used to evaluate the longitudinal relaxation timeT1as well as the zero-quantum relaxation timeTZQby fitting the theoretically predicted curve to the experimental data. The evaluated proton relaxation timesT1andTZQin citrate differ strongly:T1= 770 ms,TZQ= 1300 ms.

  9. Relaxation times of the two-phonon processes with spin-flip and spin-conserving in quantum dots

    SciTech Connect

    Wang, Zi-Wu; Liu, Lei; Li, Shu-Shen

    2014-04-07

    We perform a theoretical investigation on the two-phonon processes of the spin-flip and spin-conserving relaxation in quantum dots in the frame of the Huang-Rhys' lattice relaxation model. We find that the relaxation time of the spin-flip is two orders of magnitude longer than that of the spin-conserving, which is in agreement with previous experimental measurements. Moreover, the opposite variational trends of the relaxation time as a function of the energy separation for two-phonon processes are obtained in different temperature regime. The relaxation times display the oscillatory behaviors at the demarcation point with increasing magnetic field, where the energy separation matches the optical phonon energy and results in the optical phonon resonance. These results are useful in understanding the intraband levels' relaxation in quantum dots and could be helpful in designing photoelectric and spin-memory devices.

  10. ESR lineshape and {sup 1}H spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals – Joint analysis

    SciTech Connect

    Kruk, D.; Hoffmann, S. K.; Goslar, J.; Lijewski, S.; Kubica-Misztal, A.; Korpała, A.; Oglodek, I.; Moscicki, J.; Kowalewski, J.; Rössler, E. A.

    2013-12-28

    Electron Spin Resonance (ESR) spectroscopy and Nuclear Magnetic Relaxation Dispersion (NMRD) experiments are reported for propylene glycol solutions of the nitroxide radical: 4-oxo-TEMPO-d{sub 16} containing {sup 15}N and {sup 14}N isotopes. The NMRD experiments refer to {sup 1}H spin-lattice relaxation measurements in a broad frequency range (10 kHz–20 MHz). A joint analysis of the ESR and NMRD data is performed. The ESR lineshapes give access to the nitrogen hyperfine tensor components and the rotational correlation time of the paramagnetic molecule. The NMRD data are interpreted in terms of the theory of paramagnetic relaxation enhancement in solutions of nitroxide radicals, recently presented by Kruk et al. [J. Chem. Phys. 138, 124506 (2013)]. The theory includes the effect of the electron spin relaxation on the {sup 1}H relaxation of the solvent. The {sup 1}H relaxation is caused by dipole-dipole interactions between the electron spin of the radical and the proton spins of the solvent molecules. These interactions are modulated by three dynamic processes: relative translational dynamics of the involved molecules, molecular rotation, and electron spin relaxation. The sensitivity to rotation originates from the non-central positions of the interacting spin in the molecules. The electronic relaxation is assumed to stem from the electron spin–nitrogen spin hyperfine coupling, modulated by rotation of the radical molecule. For the interpretation of the NMRD data, we use the nitrogen hyperfine coupling tensor obtained from ESR and fit the other relevant parameters. The consistency of the unified analysis of ESR and NMRD, evaluated by the agreement between the rotational correlation times obtained from ESR and NMRD, respectively, and the agreement of the translation diffusion coefficients with literature values obtained for pure propylene glycol, is demonstrated to be satisfactory.

  11. Electron spin resonance and muon spin relaxation studies of single molecule magnets

    NASA Astrophysics Data System (ADS)

    Blundell, Stephen

    2005-03-01

    We use a combination of electron spin resonance, muon-spin relaxation and SQUID magnetometry to study polycrystalline and single crystal samples of various novel single molecule magnets (SMMs). We also describe a theoretical framework which can be used to analyse the results from each technique. Electron spin resonance measurements are performed using a millimetre vector network analyser and data are presented on several SMM systems using microwave frequencies from 40-300 GHz. Muon-spin relaxation measurements have been performed on several SMM systems in applied longitudinal magnetic field and in temperatures down to 20 mK. The results suggest that dynamic local magnetic field fluctuations are responsible for the relaxation of the muon spin ensemble. We discuss what can be learned from these experiments concerning SMMs and suggest experiments which can probe the quantum nature of SMMs. (Work in collaboration with S Sharmin, T Lancaster, A Ardavan, F L Pratt, E J L McInnes and R E P Winpenny) References: S. J. Blundell and F. L. Pratt, J. Phys.: Condens. Matter 16, R771 (2004); T. Lancaster et al., J. Phys.: Condens. Matter 16, S4563 (2004); S. Sharmin et al., Appl. Phys. Lett. in press.

  12. Interactions of /sup 14/N:/sup 15/N stearic acid spin-label pairs: effects of host lipid alkyl chain length and unsaturation

    SciTech Connect

    Feix, J.B.; Yin, J.J.; Hyde, J.S.

    1987-06-30

    Electron-electron double resonance (ELDOR) and saturation recovery electron paramagnetic resonance (EPR) spectroscopy have been employed to examine the interactions of /sup 14/N:/sup 15/N stearic acid spin-label pairs in fluid-phase model membrane bilayers composed of a variety of phospholipids. The (/sup 14/N)-16-doxylstearate:(/sup 15/N)-16-doxylstearate (16:16) pair was utilized to measure lateral diffusion of the spin-labels, while the (/sup 14/N)-16-doxylstearate:(/sup 15/N)-5-doxylstearate (16:5) pair provided information on vertical fluctuations of the 16-doxylstearate nitroxide moiety toward the membrane surface. Three saturated host lipids of varying alkyl chain length (dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC)), an ..cap alpha..-saturated, ..beta..-unsaturated lipid (1-palmitoyl-2-oleoylphosphatidylcholine (POPC)), and phosphatidylcholine from a natural source (egg yolk phosphatidylcholine (egg PC)) were utilized as host lipids. Lateral diffusion of the stearic acid spin-labels was only slightly affected by alkyl chain length at a given reduced temperature (T/sub r/) in the saturated host lipids but was significantly decreased in POPC at the same T/sub r/. Lateral diffusion in DMPC, POPC, and egg PC was quite similar at 37/sup 0/C. A strong correlation was noted between lateral diffusion constants and rotational mobility of (/sup 14/N)-16-doxylstearate. Vertical fluctuations were likewise only slightly influenced by alklyl chain length but were strongly diminished in POPC and egg PC relative to the saturated systems. This diminution of the 16:5 interaction was observed even under conditions where no differences were discernible by conventional EPR.

  13. A fast determination method for transverse relaxation of spin-exchange-relaxation-free magnetometer

    SciTech Connect

    Lu, Jixi Qian, Zheng; Fang, Jiancheng

    2015-04-15

    We propose a fast and accurate determination method for transverse relaxation of the spin-exchange-relaxation-free (SERF) magnetometer. This method is based on the measurement of magnetic resonance linewidth via a chirped magnetic field excitation and the amplitude spectrum analysis. Compared with the frequency sweeping via separate sinusoidal excitation, our method can realize linewidth determination within only few seconds and meanwhile obtain good frequency resolution. Therefore, it can avoid the drift error in long term measurement and improve the accuracy of the determination. As the magnetic resonance frequency of the SERF magnetometer is very low, we include the effect of the negative resonance frequency caused by the chirp and achieve the coefficient of determination of the fitting results better than 0.998 with 95% confidence bounds to the theoretical equation. The experimental results are in good agreement with our theoretical analysis.

  14. A fast determination method for transverse relaxation of spin-exchange-relaxation-free magnetometer.

    PubMed

    Lu, Jixi; Qian, Zheng; Fang, Jiancheng

    2015-04-01

    We propose a fast and accurate determination method for transverse relaxation of the spin-exchange-relaxation-free (SERF) magnetometer. This method is based on the measurement of magnetic resonance linewidth via a chirped magnetic field excitation and the amplitude spectrum analysis. Compared with the frequency sweeping via separate sinusoidal excitation, our method can realize linewidth determination within only few seconds and meanwhile obtain good frequency resolution. Therefore, it can avoid the drift error in long term measurement and improve the accuracy of the determination. As the magnetic resonance frequency of the SERF magnetometer is very low, we include the effect of the negative resonance frequency caused by the chirp and achieve the coefficient of determination of the fitting results better than 0.998 with 95% confidence bounds to the theoretical equation. The experimental results are in good agreement with our theoretical analysis.

  15. Nuclear Spin-Lattice Relaxation Times from Continuous Wave NMR Spectroscopy.

    ERIC Educational Resources Information Center

    Wooten, Jan B.; And Others

    1979-01-01

    The experiment described, suitable for undergraduate physical chemistry laboratories, illustrates the general principles of relaxation and introduces the nmr concepts of saturation and spin-inversion. (BB)

  16. The Spin-Lattice Relaxation of Hyperpolarized 89Y Complexes

    NASA Astrophysics Data System (ADS)

    Jindal, Ashish; Lumata, Lloyd; Xing, Yixun; Merritt, Matthew; Zhao, Piyu; Malloy, Craig; Sherry, Dean; Kovacs, Zoltan

    2011-03-01

    The low sensitivity of NMR can be overcome by dynamic nuclear polarization (DNP). However, a limitation to the use of hyperpolarized materials is the signal decay due to T1 relaxation. Among NMR-active nuclei, 89 Y is potentially valuable in medical imaging because in chelated form, pH-sensitive agents can be developed. 89 Y also offers many attractive features -- 100 % abundance, a 1/2 spin, and a long T1 , up to 10 min. Yet, developing new 89 Y complexes with even longer T1 values is desirable. Designing such complexes relies upon understanding the mechanism(s) responsible for T1 relaxation. We report an approach to hyperpolarized T1 measurements that enabled an analysis of relaxation mechanisms by selective deuteration of the ligand backbone, the solvent or both. Hyperpolarized 89 Y -- DTPA, DOTA, EDTA, and deuterated EDTA complexes were studied. Results suggest that substitution of low-gamma nuclei on the ligand backbone as opposed to that of the solvent most effectively increase the 89 Y T1 . These results are encouraging for in vivo applications as the presence of bound water may not dramatically affect the T1 .

  17. Sub-Shot-Noise Magnetometry with a Correlated Spin-Relaxation Dominated Alkali-Metal Vapor

    SciTech Connect

    Kominis, I. K.

    2008-02-22

    Spin noise sets fundamental limits to the precision of measurements using spin-polarized atomic vapors, such as performed with sensitive atomic magnetometers. Spin squeezing offers the possibility to extend the measurement precision beyond the standard quantum limit of uncorrelated atoms. Contrary to current understanding, we show that, even in the presence of spin relaxation, spin squeezing can lead to a significant reduction of spin noise, and hence an increase in magnetometric sensitivity, for a long measurement time. This is the case when correlated spin relaxation due to binary alkali-atom collisions dominates independently acting decoherence processes, a situation realized in thermal high atom-density magnetometers and clocks.

  18. Electron spin lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

    NASA Astrophysics Data System (ADS)

    Sato, Hideo; Bottle, Steven E.; Blinco, James P.; Micallef, Aaron S.; Eaton, Gareth R.; Eaton, Sandra S.

    2008-03-01

    Electron spin-lattice relaxation rates, 1/ T1, at X-band of nitroxyl radicals (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl and 3-carbamoyl-2,2,5,5-tetramethylpyrrolin-1-oxyl) in glass-forming solvents (decalin, glycerol, 3-methylpentane, o-terphenyl, 1-propanol, sorbitol, sucrose octaacetate, and 1:1 water:glycerol) at temperatures between 100 and 300 K were measured by long-pulse saturation recovery to investigate the relaxation processes in slow-to-fast tumbling regimes. A subset of samples was also studied at lower temperatures or at Q-band. Tumbling correlation times were calculated from continuous wave lineshapes. Temperature dependence and isotope substitution ( 2H and 15N) were used to distinguish the contributions of various processes. Below about 100 K relaxation is dominated by the Raman process. At higher temperatures, but below the glass transition temperature, a local mode process makes significant contributions. Above the glass transition temperature, increased rates of molecular tumbling modulate nuclear hyperfine and g anisotropy. The contribution from spin rotation is very small. Relaxation rates at X-band and Q-band are similar. The dependence of 1/ T1 on tumbling correlation times fits better with the Cole-Davidson spectral density function than with the Bloembergen-Purcell-Pound model.

  19. Spin relaxation in hole-doped transition metal dichalcogenides with the crystal defects

    NASA Astrophysics Data System (ADS)

    Habe, Tetsuro; Koshino, Mikito

    We theoretically investigate the electronic spin relaxation effect in the hole-doped monolayer and bilayer transition-metal dichalcogenides in the presence of the crystal defects. We simulate lattice vacancies in the multi-orbital tight-binding model obtained by the first-principle method and actually estimate the spin relaxation rate by using the tight-binding model. In the monolayer, the spin-relaxation time is found to be much longer than the momentum relaxation time, and this is attributed to the fact that the spin hybridization in the band structure is suppressed by the mirror reflection symmetry. The bilayer TMD has a much shorter spin relaxation time in contrast because of the stronger spin hybridization due to the absence of the mirror symmetry.

  20. Low microwave-amplitude ESR spectroscopy: measuring spin-relaxation interactions of moderately immobilized spin labels in proteins.

    PubMed

    Hedin, Eva M K; Hult, Karl; Mouritsen, Ole G; Høyrup, Pernille

    2004-08-31

    Electron spin resonance (ESR) spectroscopy in combination with site-directed spin labeling (SDSL) is a powerful tool for determining protein structure, dynamics and interactions. We report here a method for determining interactions between spin labels and paramagnetic relaxation agents, which is performed under subsaturating conditions. The low microwave-field amplitude employed (h(1)<0.36 G) only requires standard, commercially available ESR equipment. The effect of relaxation enhancement on the spin-spin-relaxation time, T(2e), is measured by this method, and compared to classical progressive power saturation performed on a free spin label, (1-oxyl-2,2,5,5-tetramethyl-Delta(3)-pyrroline-3-methyl)methanethiosulfonate (MTSL), and a spin-labeled protein (Thermomyces lanuginosa lipase, TLL-I252C), employing the water-soluble relaxation agent chromium(III) oxalate (Crox) in concentrations between 0-10 mM. The low-amplitude theory showed excellent agreement with that of classical power saturation in quantifying Crox-induced relaxation enhancement. Low-amplitude measurements were then performed using a standard resonator, with Crox, on 11 spin-labeled TLL mutants displaying rotational correlation times in the motional narrowing regime. All spin-labeled proteins exhibited significant changes in T(2e). We postulate that this novel method is especially suitable for studying moderately immobilized spin labels, such as those positioned at exposed sites in a protein. This method should prove useful for research groups with access to any ESR instrumentation.

  1. The complete set of spin observables for the (13)C(polarized proton, polarized neutron)(13)N and (15)N(polarized proton, polarized neutron)(15)O reactions

    NASA Astrophysics Data System (ADS)

    Du, Qun Qun

    1998-12-01

    The 13C(p,n)13N and 15N(p,n)15O reactions have been a puzzle for more than ten years. The ground state transitions are Jπ=1/2- to Jπ=1/2-. These are 'mixed' transitions because they can involve quantum number changes either (/Delta T=1,/ /Delta J=0,/ /Delta/pi=0,/ /Delta S=0), or (/Delta T=1,/ /Delta J=1,/ /Delta/pi=0,/ /Delta S=1); these quantum number changes are refered to as 'Fermi' and 'Gamow-Teller' respectively. Because the quantum number changes are the same as for Fermi and Gamow-Teller beta decay. From the systematics of (p,n) and (n,p) reactions on pure Fermi transitions (e.g. 0 + to 0+) and pure Gamow-Teller transitions (e.g. 0+ to 1+), calibrations have been established of cross section per unit B(F) or unit B(GT), where 'B' refers to doubly reduced matrix elements extracted from beta decay. However, cross sections for the 13C(p,n)13N(g.s.) and 15N(p,n)15O(g.s.) reactions are substantially larger than one would then predict from the known B(F)s and B(GT)s for these transitions. To explore this anomaly, spin observables were used to extract separately the Fermi and Gamow-Teller cross sections for these reactions. To acquire the complete sets of polarization- transfer observables, a new neutron polarimeter was designed, built, commissioned and calibrated. This polarimeter, call the '2π polarimeter' because of its complete azimuthal coverage for scattered neutrons, has very good position and timing resolution (354 ps). The complete sets of spin-transfer coefficients Dij for 13C(p,n)13N (at 0o , 5.5o , and 11o ) and 15N(p,n)15O (at 0o ) at 135 MeV were measured. Following the formalism of Ichimura and Kawahigashi, we extracted the spin-longitudinal, and spin-transverse and spin-independent responses D0,/ Dq,/ Dn and Dp from the measured Dijs. The F and GT fractions of the (p,n) cross sections are then extracted as f F=D0 and fGT=Dn+Dp+Dq=1- d0. Values of Dk for both the 13C(p,n)13N(g.s) and 15N(p,n)15O(g.s.) were extracted. From these responses, we

  2. Nuclear spin-spin relaxation in 3He-Ne films

    NASA Astrophysics Data System (ADS)

    Sullivan, Neil S.; Stachiowak, Piotr; Parks, Charles

    2003-05-01

    NMR measurements of the nuclear spin-spin relaxation times are reported for commensurate monolayers of 3He and 3He-Ne films on boron nitride for temperatures 0.1spin exchange term. Values of the vacancy formation energy for the monolayer coverage and the atom-vacancy exchange rate are also obtained from the experimental observations.

  3. Electron spin relaxation dynamics in GaN: influence of temperature, doping density, and crystal orientation

    NASA Astrophysics Data System (ADS)

    Buß, J. H.; Rudolph, J.; Starosielec, S.; Schaefer, A.; Semond, F.; Hägele, D.

    2013-03-01

    We present a systematic study of electron spin relaxation in wurtzite GaN. Fast relaxation is caused by a Rashba effective magnetic field that linearly depends on the electron momentum k. The field prevents spin lifetimes to exceed 50 ps at room temperature and is the origin of an anisotropic spin relaxation tensor that we evidence by magnetic field dependent magneto-optical pump-probe measurements. In addition, the spin lifetime depends - as compared to GaAs - weaker on temperature and doping density. We give a fully analytical description of both effects based on D'yakonov-Perel' theory that describes our results quantitatively without any fitting parameter.

  4. Electron spin echo and spin relaxation of low-symmetry Mn(2+)-complexes in ammonium oxalate monohydrate single crystal.

    PubMed

    Hoffmann, Stanisław K; Lijewski, Stefan; Goslar, Janina; Mielniczek-Brzóska, Ewa

    2014-09-01

    Pulse EPR experiments were performed on low concentration Mn(2+) ions in ammonium oxalate monohydrate single crystals at X-band, in the temperature range 4.2-60K at crystal orientation close to the D-tensor z-axis. Hyperfine lines of the resolved spin transitions were selectively excited by short nanosecond pulses. Electron spin echo signal was not observed for the low spin transition (+5/2↔+3/2) suggesting a magnetic field threshold for the echo excitation. Echo appears for higher spin transitions with amplitude, which grows with magnetic field. Opposite behavior displays amplitude of echo decay modulations, which is maximal at low field and negligible for high field spin transitions. Electron spin-lattice relaxation was measured by the pulse saturation method. After the critical analysis of possible relaxation processes it was concluded that the relaxation is governed by Raman T(7)-process. The relaxation is the same for all spin transitions except the lowest temperatures (below 20K) where the high field transitions (-3/2↔-1/2) and (-5/2↔-3/2) have a slower relaxation rate. Electron spin echo dephasing is produced by electron spectral diffusion mainly, with a small contribution from instantaneous diffusion for all spin transitions. For the highest field transition (-5/2↔-3/2) an additional contribution from nuclear spectral diffusion appears with resonance type enhancement at low temperatures.

  5. Observation and modelling of ferromagnetic contact-induced spin relaxation in Hanle spin precession measurements

    NASA Astrophysics Data System (ADS)

    O'Brien, L.; Spivak, D.; Krueger, N.; Peterson, T. A.; Erickson, M. J.; Bolon, B.; Geppert, C. C.; Leighton, C.; Crowell, P. A.

    2016-09-01

    In the nonlocal spin valve (NLSV) geometry, four-terminal electrical Hanle effect measurements have the potential to provide a particularly simple determination of the lifetime (τs) and diffusion length (λN) of spins injected into nonmagnetic (N) materials. Recent papers, however, have demonstrated that traditional models typically used to fit such data provide an inaccurate measurement of τs in ferromagnet (FM)/N metal devices with low interface resistance, particularly when the separation of the source and detector contacts is small. In the transparent limit, this shortcoming is due to the back diffusion and subsequent relaxation of spins within the FM contacts, which is not properly accounted for in standard models of the Hanle effect. Here we have used the separation dependence of the spin accumulation signal in NLSVs with multiple FM/N combinations, and interfaces in the diffusive limit, to determine λN in traditional spin valve measurements. We then compare these results to Hanle measurements as analyzed using models that either include or exclude spin sinking. We demonstrate that differences between the spin valve and Hanle measurements of λN can be quantitatively modelled provided that both the FM contact-induced isotropic spin sinking and the full three-dimensional geometry of the devices, which is particularly important at small contact separations, are accounted for. We find, however, that considerable difficulties persist, in particular due to the sensitivity of fitting to the contact interface resistance and the FM contact magnetization rotation, in precisely determining λN with the Hanle technique alone, particularly at small contact separations.

  6. 15N Hyperpolarization by Reversible Exchange Using SABRE-SHEATH

    PubMed Central

    2016-01-01

    NMR signal amplification by reversible exchange (SABRE) is a NMR hyperpolarization technique that enables nuclear spin polarization enhancement of molecules via concurrent chemical exchange of a target substrate and parahydrogen (the source of spin order) on an iridium catalyst. Recently, we demonstrated that conducting SABRE in microtesla fields provided by a magnetic shield enables up to 10% 15N-polarization (Theis, T.; et al. J. Am. Chem. Soc.2015, 137, 1404). Hyperpolarization on 15N (and heteronuclei in general) may be advantageous because of the long-lived nature of the hyperpolarization on 15N relative to the short-lived hyperpolarization of protons conventionally hyperpolarized by SABRE, in addition to wider chemical shift dispersion and absence of background signal. Here we show that these unprecedented polarization levels enable 15N magnetic resonance imaging. We also present a theoretical model for the hyperpolarization transfer to heteronuclei, and detail key parameters that should be optimized for efficient 15N-hyperpolarization. The effects of parahydrogen pressure, flow rate, sample temperature, catalyst-to-substrate ratio, relaxation time (T1), and reversible oxygen quenching are studied on a test system of 15N-pyridine in methanol-d4. Moreover, we demonstrate the first proof-of-principle 13C-hyperpolarization using this method. This simple hyperpolarization scheme only requires access to parahydrogen and a magnetic shield, and it provides large enough signal gains to enable one of the first 15N images (2 × 2 mm2 resolution). Importantly, this method enables hyperpolarization of molecular sites with NMR T1 relaxation times suitable for biomedical imaging and spectroscopy. PMID:25960823

  7. Hole spin relaxation in InAs/GaAs quantum dot molecules.

    PubMed

    Segarra, C; Climente, J I; Rajadell, F; Planelles, J

    2015-10-21

    We calculate the spin-orbit induced hole spin relaxation between Zeeman sublevels of vertically stacked InAs quantum dots. The widely used Luttinger-Kohn Hamiltonian, which considers coupling of heavy- and light-holes, reveals that hole spin lifetimes (T1) of molecular states significantly exceed those of single quantum dot states. However, this effect can be overcome when cubic Dresselhaus spin-orbit interaction is strong. Misalignment of the dots along the stacking direction is also found to be an important source of spin relaxation. PMID:26418483

  8. Impurities and electron spin relaxations in nanodiamonds studied by multi-frequency electron spin resonance

    NASA Astrophysics Data System (ADS)

    Cho, Franklin; Takahashi, Susumu

    2014-03-01

    Nano-sized diamond or nanodiamond is a fascinating material for potential applications of fluorescence imaging and magnetic sensing of biological systems via nitrogen-vacancy defect centers in diamonds. Sensitivity of the magnetic sensing strongly depends on coupling to surrounding environmental noises, thus understanding of the environment is critical to realize the application. In the present study, we employ multi-frequency (X-band, 115 GHz and 230 GHz) continuous-wave (cw) and pulsed electron spin resonance (ESR) spectroscopy to investigate impurity contents and spin relaxation properties in various sizes of nanodiamonds. Spectra taken with our home-built 230/115 GHz cw/pulsed ESR spectrometer shows presence of two major impurity contents; single substitutional nitrogen impurities (P1) also common in bulk diamonds and paramagnetic impurities (denoted as X) unique to nanodiamonds. The ESR measurement also shows a strong dependence of the population ratio between P1 and X on particle size. Furthermore, we will discuss the nature of spin-lattice relaxation time T1 of nanodiamonds studied by pulsed ESR measurements at X-band, 115 GHz and 230 GHz.

  9. Re-examination of the Elliott-Yafet spin-relaxation mechanism

    NASA Astrophysics Data System (ADS)

    Baral, Alexander; Vollmar, Svenja; Kaltenborn, Steffen; Schneider, Hans Christian

    2016-02-01

    We analyze spin-dependent carrier dynamics due to incoherent electron-phonon scattering, which is commonly referred to as Elliott-Yafet (EY) spin-relaxation mechanism. For this mechanism one usually distinguishes two contributions: (1) from the spin-diagonal electrostatic interaction together with spin-mixing in the wave functions, which is often called the Elliott contribution, and (2) the phonon-modulated spin-orbit interaction, which is often called the Yafet or Overhauser contribution. By computing the reduced electronic density matrix, we improve Yafet’s original calculation, which neglects the spin-mixing in the single-particle states for the determination of the ensemble spin. The important novel quantity in our calculation is a torque operator that determines the spin dynamics due to incoherent scattering. The contribution (1) to this torque vanishes exactly. From this general result, we derive a modified expression for the EY spin relaxation time for Kramers degenerate bands.

  10. Strain-induced reduction of surface roughness dominated spin relaxation in MOSFETs

    SciTech Connect

    Osintsev, Dmitri; Stanojevic, Zlatan; Baumgartner, Oskar; Sverdlov, Viktor; Selberherr, Siegfried

    2013-12-04

    Semiconductor spintronics is a rapidly developing field with large impact on microelectronics. Using spin may help to reduce power consumption and increase computational speed. Silicon is perfectly suited for spin-based applications. It is characterized by a weak spin-orbit interaction which should result in a long spin lifetime. However, recent experiments indicate the lifetime is greatly reduced in gated structures. Thus, understanding the peculiarities of the spin-orbit effects on the subband structure and details of the spin propagation in surface layers and thin silicon films is urgently needed. We investigate the contribution of the spin-orbit interaction to the equivalent valley splitting and calculate the spin relaxation matrix elements by using a perturbative k ⋅p approach. We demonstrate that applying uniaxial stress along the [110] direction may considerably suppress electron spin relaxation in silicon surface layers and thin films.

  11. Temperature Dependence of Electron Spin Relaxation of 2,2-diphenyl-1-picrylhydrazyl in Polystyrene

    PubMed Central

    Meyer, Virginia; Eaton, Sandra S.; Eaton, Gareth R.

    2012-01-01

    The electron spin relaxation rates for the stable radical DPPH (2,2-diphenyl-1-picrylhydrazyl) doped into polystyrene were studied by inversion recovery and electron spin echo at X-band and Q-band between 20 and 295 K. At low concentration (340 μM, 0.01%) spin-lattice relaxation was dominated by the Raman process and a local mode. At high concentration (140 mM, 5%) relaxation is orders of magnitude faster than at the lower concentration, and 1/T1 is approximately linearly dependent on temperature. Spin lattice relaxation rates are similar at X-band and Q-band. The temperature dependence of spin echo dephasing was faster at about 140 K than at higher or lower temperatures, which is attributed to a wagging motion of the phenyl groups. PMID:23565040

  12. Picosecond spin relaxation in low-temperature-grown GaAs

    SciTech Connect

    Uemura, M.; Honda, K.; Yasue, Y.; Tackeuchi, A.; Lu, S. L.; Dai, P.

    2014-03-24

    The spin relaxation process of low-temperature-grown GaAs is investigated by spin-dependent pump and probe reflectance measurements with a sub-picosecond time resolution. Two very short carrier lifetimes of 2.0 ps and 28 ps, which can be attributed to nonradiative recombinations related to defects, are observed at 10 K. The observed spin polarization shows double exponential decay with spin relaxation times of 46.2 ps (8.0 ps) and 509 ps (60 ps) at 10 K (200 K). The observed picosecond spin relaxation, which is considerably shorter than that of conventional GaAs, indicates the strong relevance of the Elliott-Yafet process as the spin relaxation mechanism. For the first (second) spin relaxation component, the temperature and carrier density dependences of the spin relaxation time indicate that the Bir-Aronov-Pikus process is also effective at temperatures between 10 K and 77 K, and that the D'yakonov-Perel’ process is effective between 125 K (77 K) and 200 K.

  13. A unified theory of spin-relaxation due to spin-orbit coupling in metals and semiconductors

    PubMed Central

    Boross, Péter; Dóra, Balázs; Kiss, Annamária; Simon, Ferenc

    2013-01-01

    Spintronics is an emerging paradigm with the aim to replace conventional electronics by using electron spins as information carriers. Its utility relies on the magnitude of the spin-relaxation, which is dominated by spin-orbit coupling (SOC). Yet, SOC induced spin-relaxation in metals and semiconductors is discussed for the seemingly orthogonal cases when inversion symmetry is retained or broken by the so-called Elliott-Yafet and D'yakonov-Perel' spin-relaxation mechanisms, respectively. We unify the two theories on general grounds for a generic two-band system containing intra- and inter-band SOC. While the previously known limiting cases are recovered, we also identify parameter domains when a crossover occurs between them, i.e. when an inversion symmetry broken state evolves from a D'yakonov-Perel' to an Elliott-Yafet type of spin-relaxation and conversely for a state with inversional symmetry. This provides an ultimate link between the two mechanisms of spin-relaxation. PMID:24252975

  14. Spin relaxation time dependence on optical pumping intensity in GaAs:Mn

    SciTech Connect

    Burobina, V.; Binek, Ch.

    2014-04-28

    We analyze the dependence of electron spin relaxation time on optical pumping intensity in a partially compensated acceptor semiconductor GaAs:Mn using analytic solutions for the kinetic equations of the charge carrier concentrations. Our results are applied to previous experimental data of spin-relaxation time vs. excitation power for magnetic concentrations of approximately 10{sup 17} cm{sup −3}. The agreement of our analytic solutions with the experimental data supports the mechanism of the earlier-reported atypically long electron-spin relaxation time in the magnetic semiconductor.

  15. A study of molecular dynamics and freezing phase transition in tissues by proton spin relaxation.

    PubMed Central

    Rustgi, S N; Peemoeller, H; Thompson, R T; Kydon, D W; Pintar, M M

    1978-01-01

    Muscle, spleen, and kidney tissues from 4-wk-old C57 black mice were studied by proton magnetic resonance. Spin-lattice relaxation times at high fields and in the rotating frame, as well as the spin-spin relaxation times, are reported as a function of temperature in the liquid and frozen phase. Motions of large molecules and of water molecules and their changes at the freezing phase transition are studied. The shortcomings of the two-state fast-exchange relaxation model are discussed. PMID:667294

  16. Spin-heat relaxation and thermospin diffusion in atomic Bose and Fermi gases

    NASA Astrophysics Data System (ADS)

    Wong, Clement H.; Stoof, H. T. C.; Duine, R. A.

    2015-04-01

    We study spin-dependent heat transport in quantum gases, focusing on transport phenomena related to pure spin currents and spin-dependent temperatures. Using the Boltzmann equation, we compute the coupled spin-heat transport coefficients as a function of temperature and interaction strength for energy-dependent s -wave scattering. We address the issue of whether spin-dependent temperatures can be sustained on a time and length scale relevant for experiments by computing the spin-heat relaxation time and diffusion length. We find that the time scale for spin-heat relaxation time diverges at low temperatures for both bosons and fermions, indicating that the concept of spin-heat accumulation is well defined for degenerate gases. For bosons, we find power-law behavior on approach to Bose condensation above the critical temperature, as expected from the theory of dynamical critical phenomena.

  17. Nuclear Spin Relaxation and Molecular Interactions of a Novel Triazolium-Based Ionic Liquid

    SciTech Connect

    Allen, Jesse J; Schneider, Yanika; Kail, Brian W; Luebke, David R; Nulwala, Hunaid; Damodaran, Krishnan

    2013-04-11

    Nuclear spin relaxation, small-angle X-ray scattering (SAXS), and electrospray ionization mass spectrometry (ESI-MS) techniques are used to determine supramolecular arrangement of 3-methyl-1-octyl-4-phenyl-1H-triazol-1,2,3-ium bis(trifluoromethanesulfonyl)imide [OMPhTz][Tf{sub 2}N], an example of a triazolium-based ionic liquid. The results obtained showed first-order thermodynamic dependence for nuclear spin relaxation of the anion. First-order relaxation dependence is interpreted as through-bond dipolar relaxation. Greater than first-order dependence was found in the aliphatic protons, aromatic carbons (including nearest neighbors), and carbons at the end of the aliphatic tail. Greater than first order thermodynamic dependence of spin relaxation rates is interpreted as relaxation resulting from at least one mechanism additional to through-bond dipolar relaxation. In rigid portions of the cation, an additional spin relaxation mechanism is attributed to anisotropic effects, while greater than first order thermodynamic dependence of the octyl side chain’s spin relaxation rates is attributed to cation–cation interactions. Little interaction between the anion and the cation was observed by spin relaxation studies or by ESI-MS. No extended supramolecular structure was observed in this study, which was further supported by MS and SAXS. nuclear Overhauser enhancement (NOE) factors are used in conjunction with spin–lattice relaxation time (T{sub 1}) measurements to calculate rotational correlation times for C–H bonds (the time it takes for the vector represented by the bond between the two atoms to rotate by one radian). The rotational correlation times are used to represent segmental reorientation dynamics of the cation. A combination of techniques is used to determine the segmental interactions and dynamics of this example of a triazolium-based ionic liquid.

  18. Temperature dependence of the NMR spin-lattice relaxation rate for spin-1/2 chains

    NASA Astrophysics Data System (ADS)

    Coira, E.; Barmettler, P.; Giamarchi, T.; Kollath, C.

    2016-10-01

    We use recent developments in the framework of a time-dependent matrix product state method to compute the nuclear magnetic resonance relaxation rate 1 /T1 for spin-1/2 chains under magnetic field and for different Hamiltonians (XXX, XXZ, isotropically dimerized). We compute numerically the temperature dependence of the 1 /T1 . We consider both gapped and gapless phases, and also the proximity of quantum critical points. At temperatures much lower than the typical exchange energy scale, our results are in excellent agreement with analytical results, such as the ones derived from the Tomonaga-Luttinger liquid (TLL) theory and bosonization, which are valid in this regime. We also cover the regime for which the temperature T is comparable to the exchange coupling. In this case analytical theories are not appropriate, but this regime is relevant for various new compounds with exchange couplings in the range of tens of Kelvin. For the gapped phases, either the fully polarized phase for spin chains or the low-magnetic-field phase for the dimerized systems, we find an exponential decrease in Δ /(kBT ) of the relaxation time and can compute the gap Δ . Close to the quantum critical point our results are in good agreement with the scaling behavior based on the existence of free excitations.

  19. Observations of exciton and carrier spin relaxation in Be doped p-type GaAs

    SciTech Connect

    Asaka, Naohiro; Harasawa, Ryo; Tackeuchi, Atsushi; Lu, Shulong; Dai, Pan

    2014-03-17

    We have investigated the exciton and carrier spin relaxation in Be-doped p-type GaAs. Time-resolved spin-dependent photoluminescence (PL) measurements revealed spin relaxation behaviors between 10 and 100 K. Two PL peaks were observed at 1.511 eV (peak 1) and 1.497 eV (peak 2) at 10 K, and are attributed to the recombination of excitons bound to neutral Be acceptors (peak 1) and the band-to-acceptor transition (peak 2). The spin relaxation times of both PL peaks were measured to be 1.3–3.1 ns at 10–100 K, and found to originate from common electron spin relaxation. The observed existence of a carrier density dependence of the spin relaxation time at 10–77 K indicates that the Bir-Aronov-Pikus process is the dominant spin relaxation mechanism.

  20. Nuclear magnetic relaxation by the dipolar EMOR mechanism: Three-spin systems

    NASA Astrophysics Data System (ADS)

    Chang, Zhiwei; Halle, Bertil

    2016-07-01

    In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. Starting from the stochastic Liouville equation, we have developed a non-perturbative theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole couplings, and Larmor frequencies. Here, we implement the general dipolar EMOR theory for a macromolecule-bound three-spin system, where one, two, or all three spins exchange with the bulk solution phase. In contrast to the previously studied two-spin system with a single dipole coupling, there are now three dipole couplings, so relaxation is affected by distinct correlations as well as by self-correlations. Moreover, relaxation can now couple the magnetizations with three-spin modes and, in the presence of a static dipole coupling, with two-spin modes. As a result of this complexity, three secondary dispersion steps with different physical origins can appear in the longitudinal relaxation dispersion profile, in addition to the primary dispersion step at the Larmor frequency matching the exchange rate. Furthermore, and in contrast to the two-spin system, longitudinal relaxation can be significantly affected by chemical shifts and by the odd-valued ("imaginary") part of the spectral density function. We anticipate that the detailed studies of two-spin and three-spin systems that have now been completed will provide the foundation for developing an approximate multi-spin dipolar EMOR theory sufficiently accurate and computationally efficient to allow quantitative molecular-level interpretation of frequency-dependent water-proton longitudinal relaxation data from biophysical model systems and soft biological tissue.

  1. Nuclear magnetic relaxation by the dipolar EMOR mechanism: Three-spin systems.

    PubMed

    Chang, Zhiwei; Halle, Bertil

    2016-07-21

    In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. Starting from the stochastic Liouville equation, we have developed a non-perturbative theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole couplings, and Larmor frequencies. Here, we implement the general dipolar EMOR theory for a macromolecule-bound three-spin system, where one, two, or all three spins exchange with the bulk solution phase. In contrast to the previously studied two-spin system with a single dipole coupling, there are now three dipole couplings, so relaxation is affected by distinct correlations as well as by self-correlations. Moreover, relaxation can now couple the magnetizations with three-spin modes and, in the presence of a static dipole coupling, with two-spin modes. As a result of this complexity, three secondary dispersion steps with different physical origins can appear in the longitudinal relaxation dispersion profile, in addition to the primary dispersion step at the Larmor frequency matching the exchange rate. Furthermore, and in contrast to the two-spin system, longitudinal relaxation can be significantly affected by chemical shifts and by the odd-valued ("imaginary") part of the spectral density function. We anticipate that the detailed studies of two-spin and three-spin systems that have now been completed will provide the foundation for developing an approximate multi-spin dipolar EMOR theory sufficiently accurate and computationally efficient to allow quantitative molecular-level interpretation of frequency-dependent water-proton longitudinal relaxation data from biophysical model systems and soft biological tissue. PMID:27448879

  2. Anomalous D'yakonov-Perel' spin relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Yu, T.; Wu, M. W.

    2013-06-01

    We report an anomalous scaling of the D’yakonov-Perel’ spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case in which the external magnetic field is perpendicular to the spin-orbit-coupling-induced effective magnetic field and its magnitude is much larger than the latter one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong-scattering limit, indicating that the D’yakonov-Perel’ spin relaxation demonstrates Elliott-Yafet-like behavior. Moreover, the transverse spin relaxation time is proportional (inversely proportional) to the momentum relaxation time in the strong- (weak-) scattering limit, both in the opposite trends against the well-established conventional D’yakonov-Perel’ spin relaxation behaviors. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.

  3. Simulated nuclear spin-lattice relaxation in Heisenberg ferrimagnets: Indirect observation of quadratic dispersion relations

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shoji

    2000-01-01

    In response to recent proton spin-relaxation time measurements on NiCu(pba)(H2O)3.2H2O with pba=1,3-propylenebis(oxamato), which is an excellent one-dimensional ferrimagnetic Heisenberg model system of spin (1,12), we study the Raman relaxation process in spin-(S,s) quantum ferrimagnets on the assumption of predominantly dipolar hyperfine interactions between protons and magnetic ions. The relaxation time T1 is formulated within the spin-wave theory and is estimated as a function of temperature and an applied field H by a quantum Monte Carlo method. The low-temperature behavior of the relaxation rate T-11 qualitatively varies with (S,s), while T-11 is almost proportional to H-1/2 due to the characteristic dispersion relations.

  4. Generation of spin-polarized currents via cross-relaxation with dynamically pumped paramagnetic impurities

    SciTech Connect

    Meriles, Carlos A.; Doherty, Marcus W.

    2014-07-14

    Key to future spintronics and spin-based information processing technologies is the generation, manipulation, and detection of spin polarization in a solid state platform. Here, we theoretically explore an alternative route to spin injection via the use of dynamically polarized nitrogen-vacancy (NV) centers in diamond. We focus on the geometry where carriers and NV centers are confined to proximate, parallel layers and use a “trap-and-release” model to calculate the spin cross-relaxation probabilities between the charge carriers and neighboring NV centers. We identify near-unity regimes of carrier polarization depending on the NV spin state, applied magnetic field, and carrier g-factor. In particular, we find that unlike holes, electron spins are distinctively robust against spin-lattice relaxation by other, unpolarized paramagnetic centers. Further, the polarization process is only weakly dependent on the carrier hopping dynamics, which makes this approach potentially applicable over a broad range of temperatures.

  5. Probing the Nuclear Spin-Lattice Relaxation Time at the Nanoscale

    NASA Astrophysics Data System (ADS)

    Wagenaar, J. J. T.; den Haan, A. M. J.; de Voogd, J. M.; Bossoni, L.; de Jong, T. A.; de Wit, M.; Bastiaans, K. M.; Thoen, D. J.; Endo, A.; Klapwijk, T. M.; Zaanen, J.; Oosterkamp, T. H.

    2016-07-01

    Nuclear spin-lattice relaxation times are measured on copper using magnetic-resonance force microscopy performed at temperatures down to 42 mK. The low temperature is verified by comparison with the Korringa relation. Measuring spin-lattice relaxation times locally at very low temperatures opens up the possibility to measure the magnetic properties of inhomogeneous electron systems realized in oxide interfaces, topological insulators, and other strongly correlated electron systems such as high-Tc superconductors.

  6. Will spin-relaxation times in molecular magnets permit quantum information processing?

    NASA Astrophysics Data System (ADS)

    Ardavan, Arzhang

    2007-03-01

    Certain computational tasks can be efficiently implemented using quantum logic, in which the information-carrying elements are permitted to exist in quantum superpositions. To achieve this in practice, a physical system that is suitable for embodying quantum bits (qubits) must be identified. Some proposed scenarios employ electron spins in the solid state, for example phosphorous donors in silicon, quantum dots, heterostructures and endohedral fullerenes, motivated by the long electron-spin relaxation times exhibited by these systems. An alternative electron-spin based proposal exploits the large number of quantum states and the non-degenerate transitions available in high spin molecular magnets. Although these advantages have stimulated vigorous research in molecular magnets, the key question of whether the intrinsic spin relaxation times are long enough has hitherto remained unaddressed. Using X-band pulsed electron spin resonance, we measure the intrinsic spin-lattice (T1) and phase coherence (T2) relaxation times in molecular nanomagnets for the first time. In Cr7M heterometallic wheels, with M = Ni and Mn, phase coherence relaxation is dominated by the coupling of the electron spin to protons within the molecule. In deuterated samples T2 reaches 3 μs at low temperatures, which is several orders of magnitude longer than the duration of spin manipulations, satisfying a prerequisite for the deployment of molecular nanomagnets in quantum information applications.

  7. Spin dynamics and relaxation in graphene dictated by electron-hole puddles

    PubMed Central

    Van Tuan, Dinh; Ortmann, Frank; Cummings, Aron W.; Soriano, David; Roche, Stephan

    2016-01-01

    The understanding of spin dynamics and relaxation mechanisms in clean graphene, and the upper time and length scales on which spin devices can operate, are prerequisites to realizing graphene-based spintronic technologies. Here we theoretically reveal the nature of fundamental spin relaxation mechanisms in clean graphene on different substrates with Rashba spin-orbit fields as low as a few tens of μeV. Spin lifetimes ranging from 50 picoseconds up to several nanoseconds are found to be dictated by substrate-induced electron-hole characteristics. A crossover in the spin relaxation mechanism from a Dyakonov-Perel type for SiO2 substrates to a broadening-induced dephasing for hBN substrates is described. The energy dependence of spin lifetimes, their ratio for spins pointing out-of-plane and in-plane, and the scaling with disorder provide a global picture about spin dynamics and relaxation in ultraclean graphene in the presence of electron-hole puddles. PMID:26876333

  8. Spin dynamics and relaxation in graphene dictated by electron-hole puddles.

    PubMed

    Tuan, Dinh Van; Ortmann, Frank; Cummings, Aron W; Soriano, David; Roche, Stephan

    2016-01-01

    The understanding of spin dynamics and relaxation mechanisms in clean graphene, and the upper time and length scales on which spin devices can operate, are prerequisites to realizing graphene-based spintronic technologies. Here we theoretically reveal the nature of fundamental spin relaxation mechanisms in clean graphene on different substrates with Rashba spin-orbit fields as low as a few tens of μeV. Spin lifetimes ranging from 50 picoseconds up to several nanoseconds are found to be dictated by substrate-induced electron-hole characteristics. A crossover in the spin relaxation mechanism from a Dyakonov-Perel type for SiO2 substrates to a broadening-induced dephasing for hBN substrates is described. The energy dependence of spin lifetimes, their ratio for spins pointing out-of-plane and in-plane, and the scaling with disorder provide a global picture about spin dynamics and relaxation in ultraclean graphene in the presence of electron-hole puddles. PMID:26876333

  9. Generalized extended Navier-Stokes theory: multiscale spin relaxation in molecular fluids.

    PubMed

    Hansen, J S

    2013-09-01

    This paper studies the relaxation of the molecular spin angular velocity in the framework of generalized extended Navier-Stokes theory. Using molecular dynamics simulations, it is shown that for uncharged diatomic molecules the relaxation time decreases with increasing molecular moment of inertia per unit mass. In the regime of large moment of inertia the fast relaxation is wave-vector independent and dominated by the coupling between spin and the fluid streaming velocity, whereas for small inertia the relaxation is slow and spin diffusion plays a significant role. The fast wave-vector-independent relaxation is also observed for highly packed systems. The transverse and longitudinal spin modes have, to a good approximation, identical relaxation, indicating that the longitudinal and transverse spin viscosities have same value. The relaxation is also shown to be isomorphic invariant. Finally, the effect of the coupling in the zero frequency and wave-vector limit is quantified by a characteristic length scale; if the system dimension is comparable to this length the coupling must be included into the fluid dynamical description. It is found that the length scale is independent of moment of inertia but dependent on the state point. PMID:24125208

  10. Electron spin relaxation can enhance the performance of a cryptochrome-based magnetic compass sensor

    NASA Astrophysics Data System (ADS)

    Kattnig, Daniel R.; Sowa, Jakub K.; Solov'yov, Ilia A.; Hore, P. J.

    2016-06-01

    The radical pair model of the avian magnetoreceptor relies on long-lived electron spin coherence. Dephasing, resulting from interactions of the spins with their fluctuating environment, is generally assumed to degrade the sensitivity of this compass to the direction of the Earth's magnetic field. Here we argue that certain spin relaxation mechanisms can enhance its performance. We focus on the flavin–tryptophan radical pair in cryptochrome, currently the only candidate magnetoreceptor molecule. Correlation functions for fluctuations in the distance between the two radicals in Arabidopsis thaliana cryptochrome 1 were obtained from molecular dynamics (MD) simulations and used to calculate the spin relaxation caused by modulation of the exchange and dipolar interactions. We find that intermediate spin relaxation rates afford substantial enhancements in the sensitivity of the reaction yields to an Earth-strength magnetic field. Supported by calculations using toy radical pair models, we argue that these enhancements could be consistent with the molecular dynamics and magnetic interactions in avian cryptochromes.

  11. Carrier spin relaxation in GaInNAsSb/GaNAsSb/GaAs quantum well

    SciTech Connect

    Asami, T.; Nosho, H.; Tackeuchi, A.; Li, L. H.; Harmand, J. C.; Lu, S. L.

    2011-12-23

    We have investigated the carrier spin relaxation in GaInNAsSb/GaNAsSb/GaAs quantum well (QW) by time-resolved photoluminescence (PL) measurement. The sample consists of an 8-nm-thick GaIn{sub 0.36}N{sub 0.006}AsSb{sub 0.015} well, 5-nm-thick GaN{sub 0.01}AsSb{sub 0.11} intermediate barriers and 100-nm-thick GaAs barriers grown by molecular beam epitaxy on a GaAs(100) substrate. The spin relaxation time and recombination lifetime at 10 K are measured to be 228 ps and 151 ps, respectively. As a reference, we have also obtained a spin relaxation time of 125 ps and a recombination lifetime of 63 ps for GaInNAs/GaNAs/GaAs QW. This result shows that crystal quality is slightly improved by adding Sb, although these short carrier lifetimes mainly originate from a nonradiative recombination. These spin relaxation times are longer than the 36 ps spin relaxation time of InGaAs/InP QWs and shorter than the 2 ns spin relaxation time of GaInNAs/GaAs QW.

  12. Application of muon spin relaxation experiment to the mixed state superconductors

    SciTech Connect

    Inui, M. ); Harshman, D.R. )

    1991-05-09

    We discuss the use of muon spin relaxation ({mu}{sup +}SR) technique to study the mixed state of superconductors. Besides the application for static vortex configurations, we argue that large vortex motion can manifest itself as a narrowed time-averaged field distribution, which in turn results in a smaller relaxation rate. A static but disordered vortex configuration can also reduce the relaxation. We summarize these arguments. 7 refs.

  13. Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy.

    PubMed

    Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

    2016-07-01

    Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as (13)C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. (13)C) and abundant I (e.g. (1)H) spins affects the measured T1S values in solid-state NMR in the absence of (1)H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance l-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions. PMID:27187211

  14. Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy.

    PubMed

    Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

    2016-07-01

    Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as (13)C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. (13)C) and abundant I (e.g. (1)H) spins affects the measured T1S values in solid-state NMR in the absence of (1)H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance l-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

  15. Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

    2016-07-01

    Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as 13C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. 13C) and abundant I (e.g. 1H) spins affects the measured T1S values in solid-state NMR in the absence of 1H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance L-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

  16. Spin relaxation in graphene with self-assembled cobalt porphyrin molecules

    NASA Astrophysics Data System (ADS)

    Omar, S.; Gurram, M.; Vera-Marun, I. J.; Zhang, X.; Huisman, E. H.; Kaverzin, A.; Feringa, B. L.; van Wees, B. J.

    2015-09-01

    In graphene spintronics, interaction of localized magnetic moments with the electron spins paves a new way to explore the underlying spin-relaxation mechanism. A self-assembled layer of organic cobalt porphyrin (CoPP) molecules on graphene provides a desired platform for such studies via the magnetic moments of porphyrin-bound cobalt atoms. In this work a study of spin-transport properties of graphene spin-valve devices functionalized with such CoPP molecules as a function of temperature via nonlocal spin-valve and Hanle spin-precession measurements is reported. For the functionalized (molecular) devices, we observe a decrease in the spin-relaxation time τs even up to 50%, which could be an indication of enhanced spin-flip scattering of the electron spins in graphene in the presence of the molecular magnetic moments. The effect of the molecular layer is masked for low-quality samples (low mobility), possibly due to dominance of Elliot-Yafet-type spin relaxation mechanisms.

  17. Dipolar Order and Spin-Lattice Relaxation in a Liquid Entrapped into Nanosize Cavities

    NASA Astrophysics Data System (ADS)

    Furman, Gregory; Goren, Shaul

    2011-12-01

    It was shown that by means of the two-pulse sequence, the spin system of a liquid entrapped into nanosize cavities can be prepared in quasi-equilibrium states of high dipolar order, which relax to thermal equilibrium with the molecular environment with a relaxation time T1d. Measurements of the inverse dipolar temperature and spin-lattice relaxation time in the local fields provide an important information about the cavity size V, its shape F, and orientation θ (with respect to the external magnetic field) of the nanopores.

  18. Study of spatial spin-modulated structures by Mössbauer spectroscopy using SpectrRelax

    SciTech Connect

    Matsnev, Mikhail E. Rusakov, Vyacheslav S.

    2014-10-27

    SpectrRelax is an application for analysis and fitting of absorption and emission Mössbauer spectra. It includes a large selection of static and relaxation spectrum models, and allows fitting and searching for optimal model parameters. Recently, we have added new models for Mössbauer spectra of nuclides in spatial spin modulated structures. In these structures, spin density or direction changes in a periodic way along a single direction, and this wave is incommensurate with the underlying lattice. The models include Spin/Charge density wave, where the shape of this wave is represented as a sum of odd harmonics, Anharmonic spin modulation where the spin direction has a cycloidal type modulation, and a Spiral-like spin structure, in which magnetic moments rotate in a plane perpendicular to the wave propagation vector, forming a spiral.

  19. Numerical Simulation of the Proton Spin-Lattice Relaxation in Bimetallic Chain Compounds

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.

    In response to recent proton spin relaxation-time measurements on a bimetallic chain compound NiCu(C7H6N2O6) (H2O)3\\cdot2H2O, we simulate the Raman relaxation process in Heisenberg alternating-spin chains on the assumption of predominantly dipolar hyperfine interactions between protons and magnetic ions. The relaxation time T1 is formulated within the spin-wave theory and is estimated as a function of temperature and an applied field H by a quantum Monte Carlo method. The low-temperature behavior of the relaxation rate T1-1 qualitatively varies with (S,s), while T1-1 is almost proportional to H-1/2 due to the characteristic dispersion relations.

  20. Spin relaxation of a short-lived radical in zero magnetic field.

    PubMed

    McKenzie, Iain

    2011-01-21

    A short-lived radical containing only one I = 1/2 nucleus, the muoniated 1,2-dicarboxyvinyl radical dianion, was produced in an aqueous solution by the reaction of muonium with the dicarboxyacetylene dianion. The identity of the radical was confirmed by measuring the muon hyperfine coupling constant (hfcc) by transverse field muon spin rotation spectroscopy and comparing this value with the hfcc obtained from DFT calculations. The muon spin relaxation rate of this radical was measured as a function of temperature in zero magnetic field by the zero field muon spin relaxation technique. The results have been interpreted using the theoretical model of Fedin et al. (J. Chem. Phys., 2003, 118, 192). The muon spin polarization decreases exponentially with time after muon implantation and the temperature dependence of the spin relaxation rate indicates that the dominant relaxation mechanism is the modulation of the anisotropic hyperfine interaction due to molecular rotation. The effective radius of the radical in solution was determined to be 1.12 ± 0.04 nm from the dependence of the muon spin relaxation rate on the temperature and viscosity of the solution, and is approximately 3.6 times larger than the value obtained from DFT calculations.

  1. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    DOE PAGES

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-24

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and 2, the time dependence of the space-integrated spin polarization P(t) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, whichmore » occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P(t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d=1 versus d=3). We investigate in detail the coordinate dependence of the time-integrated spin polarization σ(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while σ(r) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.« less

  2. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    SciTech Connect

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-24

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and 2, the time dependence of the space-integrated spin polarization P(t) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P(t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d=1 versus d=3). We investigate in detail the coordinate dependence of the time-integrated spin polarization σ(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while σ(r) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.

  3. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-01

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d -dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d =1 and 2, the time dependence of the space-integrated spin polarization P (t ) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P (t ) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d =1 versus d =3 ). Furthermore, we investigate in detail the coordinate dependence of the time-integrated spin polarization σ (r ) , which can be probed in the spin-transport experiments with spin-polarized electrodes. We demonstrate that, while σ (r ) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.

  4. Cross-Correlation Effects Involving Curie Spin Relaxation in Methyl Groups

    NASA Astrophysics Data System (ADS)

    Madhu, P. K.; Mandal, Pravat K.; Müller, Norbert

    2002-03-01

    Cross-correlation effects arising in methyl protons due to the simultaneous presence of dipole-dipole, chemical shift anisotropy, and Curie spin relaxation mechanisms in paramagnetic systems are analyzed. We assess the potential of obtaining structural constraints from the cross-correlation of Curie spin relaxation with dipolar relaxation mechanisms among methyl proton spins. By theoretical analysis and numerical simulations we characterize the transfer functions describing the interconversion processes of different ranks of multispin order. The time dependence of these processes contains a new type of structural information, the orientation of the methyl C3-axis with respect to the electron center. Experimental confirmation is found for selected methyl groups in low spin Fe3+ sperm whale myoglobin.

  5. Spin relaxation of a diffusively moving carrier in a random hyperfine field

    NASA Astrophysics Data System (ADS)

    Roundy, R. C.; Raikh, M. E.

    2014-11-01

    Relaxation, , of the average spin of a carrier in a course of hops over sites hosting random hyperfine fields is studied theoretically. In low dimensions, d =1 ,2 , the decay of average spin with time is nonexponential at all times. The origin of the effect is that for d =1 ,2 a typical random-walk trajectory exhibits numerous self-intersections. Multiple visits of the carrier to the same site accelerates the relaxation since the corresponding partial rotations of spin during these visits add up. Another consequence of self-intersections of the random-walk trajectories is that, in all dimensions, the average, , becomes sensitive to a weak magnetic field directed along z . Our analytical predictions are complemented by the numerical simulations of . The scenario of acceleration of spin relaxation due to returns applies also to the non-Markovian decoherence of a qubit surrounded by multiple fluctuators.

  6. Zeeman energy and spin relaxation in a one-electron quantum dot.

    PubMed

    Hanson, R; Witkamp, B; Vandersypen, L M K; van Beveren, L H Willems; Elzerman, J M; Kouwenhoven, L P

    2003-11-01

    We have measured the relaxation time, T1, of the spin of a single electron confined in a semiconductor quantum dot (a proposed quantum bit). In a magnetic field, applied parallel to the two-dimensional electron gas in which the quantum dot is defined, Zeeman splitting of the orbital states is directly observed by measurements of electron transport through the dot. By applying short voltage pulses, we can populate the excited spin state with one electron and monitor relaxation of the spin. We find a lower bound on T1 of 50 micros at 7.5 T, only limited by our signal-to-noise ratio. A continuous measurement of the charge on the dot has no observable effect on the spin relaxation.

  7. Temperature dependence of the spin relaxation in highly degenerate ZnO thin films

    SciTech Connect

    Prestgard, M. C.; Siegel, G.; Tiwari, A.; Roundy, R.; Raikh, M.

    2015-02-28

    Zinc oxide is considered a potential candidate for fabricating next-generation transparent spintronic devices. However, before this can be achieved, a thorough scientific understanding of the various spin transport and relaxation processes undergone in this material is essential. In the present paper, we are reporting our investigations into these processes via temperature dependent Hanle experiments. ZnO thin films were deposited on c-axis sapphire substrates using a pulsed laser deposition technique. Careful structural, optical, and electrical characterizations of the films were performed. Temperature dependent non-local Hanle measurements were carried out using an all-electrical scheme for spin injection and detection over the temperature range of 20–300 K. From the Hanle data, spin relaxation time in the films was determined at different temperatures. A detailed analysis of the data showed that the temperature dependence of spin relaxation time follows the linear-in-momentum Dyakonov-Perel mechanism.

  8. Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.

    PubMed

    Field, Timothy R

    2014-11-01

    Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties.

  9. Strong spin relaxation anisotropy in a single-electron quantum dot

    NASA Astrophysics Data System (ADS)

    Yu, Liuqi; Camenzind, L. C.; Biesinger, D. E. F.; Zimmerman, J.; Gossard, A. C.; Zumbühl, D. M.

    Spin coherence and relaxation is of crucial importance in operating spin based qubits. In a magnetic field, spins relax predominately through spin-phonon coupling mediated by spin-orbit interaction (SOI). Here we present measurements of the spin relaxation rate anisotropy in a gate defined single-electron GaAs quantum dot. The spin relaxation rate W is measured at applied magnetic fields of 4 T in the plane of the 2D electron gas. W exhibits strong anisotropy: a sinusoidal dependence on the B-field angle φ with a period of 180 degrees, as reported recently. The extrema are observed at fields pointing nearly along the [110] and [1-10] crystal axes, modulated by a factor of about 14 from minimum to maximum. The periodicity is attributed to the interplay of Rashba and Dresselhaus SOIs. To decipher the role of SOI, we perform pulsed-gate spectroscopy to extract orbital excited-state energies, and obtain very good agreement with theory also for the angular dependence W(φ) , indicating that α and β, Rashba and Dresselhaus coefficients respectively, have the same relative sign and are within 20% of each other. With controllable manipulations of the dot orbitals by varying gate voltages, it is possible to precisely extract values of α and β. Meanwhile, top- and back gates have been implemented on the device structure, which allows full electrical control over the Rashba SOI in the 2D electron gas

  10. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2

    NASA Astrophysics Data System (ADS)

    Yang, Luyi; Sinitsyn, Nikolai A.; Chen, Weibing; Yuan, Jiangtan; Zhang, Jing; Lou, Jun; Crooker, Scott A.

    2015-10-01

    The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin-valley physics. Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments, PL timescales are necessarily constrained by short-lived (3-100 ps) electron-hole recombination. Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage. Here we directly measure the coupled spin-valley dynamics in electron-doped MoS2 and WS2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3 ns at 5 K (two to three orders of magnitude longer than typical exciton recombination times). In contrast with conventional III-V or II-VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin-valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin-orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.

  11. Relaxation of electron-hole spins in strained graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Prabhakar, Sanjay; Melnik, Roderick

    2015-11-01

    We investigate the influence of magnetic field originating from the electromechanical effect on the spin-flip behaviors caused by electromagnetic field radiation in the strained graphene nanoribbons (GNRs). We show that the spin splitting energy difference (≈10 meV) due to pseudospin is much larger than the spin-orbit coupling effect (Balakrishnan et al 2013 Nat. Phys. 9 284) that might provide an evidence of broken symmetry of degeneracy. The induced spin splitting energy due to ripple waves can be further enhanced with increasing values of applied tensile edge stress for potential applications in straintronic devices. In particular, we show that the enhancement in the magnitude of the ripple waves due to externally applied tensile edge stress extends the tuning of spin-flip behaviors to larger widths of GNRs.

  12. Relaxation of electron-hole spins in strained graphene nanoribbons.

    PubMed

    Prabhakar, Sanjay; Melnik, Roderick

    2015-11-01

    We investigate the influence of magnetic field originating from the electromechanical effect on the spin-flip behaviors caused by electromagnetic field radiation in the strained graphene nanoribbons (GNRs). We show that the spin splitting energy difference (≈10 meV) due to pseudospin is much larger than the spin-orbit coupling effect (Balakrishnan et al 2013 Nat. Phys. 9 284) that might provide an evidence of broken symmetry of degeneracy. The induced spin splitting energy due to ripple waves can be further enhanced with increasing values of applied tensile edge stress for potential applications in straintronic devices. In particular, we show that the enhancement in the magnitude of the ripple waves due to externally applied tensile edge stress extends the tuning of spin-flip behaviors to larger widths of GNRs. PMID:26447532

  13. Theory of spin relaxation by translational diffusion in two-dimensional systems

    NASA Astrophysics Data System (ADS)

    Korb, J.-P.; Winterhalter, M.; McConnell, H. M.

    1984-02-01

    Spin relaxation rates T-11 and T-12 are calculated for nuclear (or electron) spins diffusing on finite two-dimensional, planar, or spherical surfaces. The spin relaxation is assumed to be due to modulation of the intermolecular dipole-dipole interactions. It is shown that the mathematical divergences encountered in a number of previous theoretical treatments of this problem for infinite planar surfaces have no physical significance; these divergences are avoided by limiting the calculations to two-dimensional systems that are finite, but that are otherwise of arbitrarily large size. The theoretical relaxation rates T-11 and T-12 for finite, planar two-dimensional systems are found to have a number of unique properties that should facilitate the interpretation of magnetic resonance spectra of molecules physically adsorbed on solid surfaces. For example, the reduction in dimensionality of rapid diffusive motion yields relaxation rates typical of slow motion in three-dimensional systems. Under certain conditions the relaxation rate T-11 is strongly dependent on the size of the two-dimensional surface on which atoms or molecules diffuse. Moreover the shape of the surface (planar or spherical), which is of particular importance in the description of the two-dimensional dynamics, can profoundly alter the frequency and temperature dependences of the spin-relaxation rates. The theory appears to be directly applicable to recent experiments by J. Tabony [Prog. Nucl. Magn. Reson. Spectrosc. 14, 1 (1980)].

  14. Wannier interpolation study of the Elliot-Yafet spin relaxation in metals

    NASA Astrophysics Data System (ADS)

    Roman, Eric; Souza, Ivo; Yates, Jonathan

    2007-03-01

    Energy states of nonmagnetic metals may be chosen to be purely spin up and down in the absence of spin-orbit coupling. Spin-orbit coupling mixes the two states by a small amount b^2. A spin-conserving interaction (e.g. electron-phonon) causes transitions between the two states, and flips the electron's spin. Some insight into this Elliot-Yafet spin relaxation mechanism can be obtained by averaging b^2 over the Fermi surface. In trivalent metals, such as aluminum, b^21 almost everywhere on the Fermi surface, except at small ``hot spot'' regions. Although the small regions of large b^2 dominate the spin relaxation process, they are difficult to capture numerically. We describe a Wannier interpolation strategy to compute . We validate it by performing ab initio calculations on aluminum, finding good agreement with previous results.^1 We also discuss interpolating ab initio electron-phonon matrix elements to compute the spin relaxation rate. J. Fabian and S. Das Sarma, Phys. Rev. Lett. 81, 5624 (1998). X. Wang, J. Yates, I. Souza, and D. Vanderbilt, Phys. Rev. B, in press (cond-mat/0608257).

  15. Suppression of spin-exchange relaxation in tilted magnetic fields within the geophysical range

    NASA Astrophysics Data System (ADS)

    Scholtes, Theo; Pustelny, Szymon; Fritzsche, Stephan; Schultze, Volkmar; Stolz, Ronny; Meyer, Hans-Georg

    2016-07-01

    We present a detailed experimental and theoretical study on the relaxation of spin coherence due to the spin-exchange mechanism arising in the electronic ground states of alkali-metal vapor atoms. As opposed to the well-explored formation of a stretched state in a longitudinal geometry (magnetic field parallel to the laser propagation direction) we employ adapted hyperfine-selective optical pumping in order to suppress spin-exchange relaxation. By comparing measurements of the intrinsic relaxation rate of the spin coherence in the ground state of cesium atoms with detailed density-matrix simulations we show that the relaxation due to spin-exchange collisions can be reduced substantially even in a tilted magnetic field of geomagnetic strength, the major application case of scalar magnetic surveying. This explains the observed striking improvement in sensitivity and further deepens the understanding of the light-narrowed Mx magnetometer, which was presented recently. Additionally, new avenues for investigating the dynamics in alkali-metal atoms governed by the spin-exchange interaction and interacting with arbitrary external fields open up.

  16. Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations

    PubMed Central

    Eckstein, Martin; Werner, Philipp

    2016-01-01

    Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid. PMID:26883536

  17. The Stern-Gerlach experiment and the effects of spin relaxation.

    PubMed

    Wennerström, Håkan; Westlund, Per-Olof

    2012-02-01

    The classical Stern-Gerlach experiment is analyzed with an emphasis on the spin dynamics. The central question asked is whether there occurs a relaxation of the spin angular momentum during the time the particle passes through the Stern-Gerlach magnet. We examine in particular the transverse relaxation, involving angular momentum exchange between the spin of the particles and the spins of the magnet. A method is presented describing relaxation effects at an individual particle level. This leads to a stochastic equation of motion for the spins. This is coupled to a classical equation of motion for the particle translation. The experimental situation is then modeled through simulations of individual trajectories using two sets of parameter choices and three different sets of initial conditions. The two main conclusions are: (A) if the coupling between the magnet and the spin is solely described by the Zeeman interaction with the average magnetic field the simulations show a clear disagreement with the experimental observation of Stern and Gerlach. (B) If one, on the other hand, also allows for a T(2) relaxation time shorter than the passage time one can obtain a practically quantitative agreement with the experimental observations. These conclusions are at variance with the standard textbook explanation of the Stern-Gerlach experiment.

  18. Silicon network structure and 29Si spin-lattice relaxation in amorphous hydrogenated silicon

    NASA Astrophysics Data System (ADS)

    Cheung, Man Ken; Petrich, Mark A.

    1992-04-01

    We report a NMR study of amorphous hydrogenated silicon (a-Si:H) that measures the 29Si spin-lattice relaxation time T1. Measurements of 29Si T1 are useful in learning about the silicon network structure and the localized states within the mobility gap. Coupling to paramagnetic dangling bonds is the predominant 29Si spin-lattice relaxation mechanism in a-Si:H. Spin flipping of paramagnetic electrons, caused by coupling to the lattice, produces fluctuating local fields that stimulate nuclear spin-lattice relaxation. By comparing our experimental results with existing theory, we find that dangling bonds are randomly distributed in device-quality materials but are inhomogeneously distributed in non-device-quality materials. We also find that there are two simultaneously occurring dangling-bond spin-lattice relaxation mechanisms: one through the spin-orbit coupling modulated by thermal excitation of ``two-level systems,'' and the other through hopping conduction between localized states near the Fermi level. Simple chemical-shift measurements are also helpful in characterizing a-Si:H. We find that the 29Si resonance shifts upfield with increasing microstructure in the material.

  19. Mechanism of Solid-State Thermolysis of Ammonia Boraine: 15N NMR Study Using Fast Magic-Angle Spinning and Dynamic Nuclear Polarization

    SciTech Connect

    Kobayashi, Takeshi; Gupta, Shalabh; Caporini, Marc A; Pecharsky, Vitalij K; Pruski, Marek

    2014-08-28

    The solid-state thermolysis of ammonia borane (NH3BH3, AB) was explored using state-of-the-art 15N solid-state NMR spectroscopy, including 2D indirectly detected 1H{15N} heteronuclear correlation and dynamic nuclear polarization (DNP)-enhanced 15N{1H} cross-polarization experiments as well as 11B NMR. The complementary use of 15N and 11B NMR experiments, supported by density functional theory calculations of the chemical shift tensors, provided insights into the dehydrogenation mechanism of AB—insights that have not been available by 11B NMR alone. Specifically, highly branched polyaminoborane derivatives were shown to form from AB via oligomerization in the “head-to-tail” manner, which then transform directly into hexagonal boron nitride analog through the dehydrocyclization reaction, bypassing the formation of polyiminoborane.

  20. Effect of surfactant and solvent on spin-lattice relaxation dynamics of magnetic nanocrystals.

    PubMed

    Maiti, Sourav; Chen, Hsiang-Yun; Chen, Tai-Yen; Hsia, Chih-Hao; Son, Dong Hee

    2013-04-25

    The effect of varying the surfactant and solvent medium on the dynamics of spin-lattice relaxation in photoexcited Fe3O4 nanocrystals has been investigated by measuring the time-dependent magnetization employing pump-probe transient Faraday rotation technique. The variation of the surfactants having surface-binding functional groups modified not only the static magnetization but also the dynamics of the recovery of the magnetization occurring via spin-lattice relaxation in the photoexcited Fe3O4 nanocrystals. The variation of the polarity and size of the solvent molecules can also influence the spin-lattice relaxation dynamics. However, the effect is limited to the nanocrystals having sufficiently permeable surfactant layer, where the small solvent molecules (e.g., water) can access the surface and dynamically modify the ligand field on the surface. PMID:23003213

  1. Nuclear Spin relaxation mediated by Fermi-edge electrons in n-type GaAs

    NASA Astrophysics Data System (ADS)

    Kotur, M.; Dzhioev, R. I.; Kavokin, K. V.; Korenev, V. L.; Namozov, B. R.; Pak, P. E.; Kusrayev, Yu. G.

    2014-03-01

    A method based on the optical orientation technique was developed to measure the nuclear-spin lattice relaxation time T 1 in semiconductors. It was applied to bulk n-type GaAs, where T 1 was measured after switching off the optical excitation in magnetic fields from 400 to 1200 G at low (< 30 K) temperatures. The spin-lattice relaxation of nuclei in the studied sample with n D = 9 × 1016 cm-3 was found to be determined by hyperfine scattering of itinerant electrons (Korringa mechanism) which predicts invariability of T 1 with the change in magnetic field and linear dependence of the relaxation rate on temperature. This result extends the experimentally verified applicability of the Korringa relaxation law in degenerate semiconductors, previously studied in strong magnetic fields (several Tesla), to the moderate field range.

  2. Resonant Scattering off Magnetic Impurities in Graphene: Mechanism for Ultrafast Spin Relaxation

    NASA Astrophysics Data System (ADS)

    Kochan, D.; Gmitra, M.; Fabian, J.

    We give a tutorial account of our recently proposed mechanism for spin relaxation based on spin-flip resonant scattering off local magnetic moments. The mechanism is rather general, working in any material with a resonant local moment, but we believe that its particular niche is graphene, whose measured spin relaxation time is 100-1000 ps. Conventional spin-orbit coupling based mechanisms (Elliott-Yafet or Dyakonov-Perel) would require large concentrations (1000 ppm) of impurities to explain this. Our mechanism needs only 1 ppm of resonant local moments, as these act as local spin hot spots: the resonant scatterers do not appear to substantially affect graphene's measured resistivity, but are dominating spin relaxation. In principle, the local moments can come from a variety of sources. Most likely would be organic molecule adsorbants or metallic adatoms. As the representative model, particularly suited for a tutorial, we consider hydrogen adatoms which are theoretically and experimentally demonstrated to yield local magnetic moments when chemisorbed on graphene. We introduce the scattering formalism and apply it to graphene, to obtain the T-matrix and spin-flip scattering rates using the generalized Fermi golden rule.

  3. Exchange-Driven Spin Relaxation in Ferromagnet-Oxide-Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Ou, Yu-Sheng; Chiu, Yi-Hsin; Harmon, N. J.; Odenthal, Patrick; Sheffield, Matthew; Chilcote, Michael; Kawakami, R. K.; Flatté, M. E.; Johnston-Halperin, E.

    2016-03-01

    We demonstrate that electron spin relaxation in GaAs in the proximity of a Fe /MgO layer is dominated by interaction with an exchange-driven hyperfine field at temperatures below 60 K. Temperature-dependent spin-resolved optical pump-probe spectroscopy reveals a strong correlation of the electron spin relaxation with carrier freeze-out, in quantitative agreement with a theoretical interpretation that at low temperatures the free-carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. As the regime of large nuclear inhomogeneity is accessible in these heterostructures for magnetic fields <3 kG , inferences from this result resolve a long-standing and contentious dispute concerning the origin of spin relaxation in GaAs at low temperature when a magnetic field is present. Further, this improved fundamental understanding clarifies the importance of future experiments probing the time-dependent exchange interaction at a ferromagnet-semiconductor interface and its consequences for spin dissipation and transport during spin pumping.

  4. Muoniated spin probes in the discotic liquid crystal HHTT: rapid electron spin relaxation in the hexagonal columnar and isotropic phases.

    PubMed

    McKenzie, Iain; Cammidge, Andrew N; Gopee, Hemant; Dilger, Herbert; Scheuermann, Robert; Stoykov, Alexey; Jayasooriya, Upali A

    2013-01-01

    Avoided level crossing muon spin resonance (ALC-μSR) spectroscopy was used to study radicals produced by the addition of the light hydrogen isotope muonium (Mu) to the discotic liquid crystal (DLC) 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT). Mu adds to the secondary carbon atoms of HHTT to produce a substituted cyclohexadienyl radical, whose identity was confirmed by comparing the measured hyperfine coupling constants with values obtained from DFT calculations. ALC-μSR spectra were obtained in the isotropic (I), hexagonal columnar (Col(h)), helical (H), and crystalline (Cr) phases. In the I and Col(h) phases the radicals, which are incorporated within the stacks of HHTT molecules as isolated paramagnetic defects, undergo extremely rapid electron spin relaxation, on the order of a hundredfold faster than in the H or Cr phases. The electron spin relaxation rate increases significantly with increasing temperature and appears to be caused by the liquidlike motion within the columns, which modulates the overlap between the π system of the radical and the π systems of the neighboring HHTT molecules, and hence, the hyperfine coupling constants. Rapid electron spin relaxation should occur for any π radical incorporated within the columns of a DLC, which may limit the utility of DLCs for future spin-based technologies.

  5. Microscopic spin dephasing and magnetization relaxation in an s-d model

    NASA Astrophysics Data System (ADS)

    Schneider, Hans Christian; Baral, Alexander

    2014-03-01

    We calculate the spin dynamics in a model of itinerant carriers coupled antiferromagnetically to a macrospin (''s-d model''). The dephasing comes in via the coupling to a phonon bath in the presence of spin-orbit coupling, which we take to be of the Bychkov-Rashba type. Using a mean-field approximation for the s-d model with an antiferromagnetic exchange coupling, we derive Boltzmann scattering integrals for itinerant-carrier spin density matrix, i.e., for the distributions and spin coherences. The spin density matrix is needed because of a constant change of the longitudinal and transverse directions during the coupled dynamics of the itinerant spins and the macrospin. Due to the Rashba spin-orbit coupling, the resulting model describes a form of Elliot-Yafet type carrier-spin relaxation due to electron-phonon scattering within an equation-of-motion formalism. We extrapolate dephasing- and magnetization times T1 and T2 and draw a comparison to phenomenological equations such as the Landau-Lifshitz or Landau-Lifshitz Gilbert equations. We then analyze the magnetization precession and relaxation of the coupled carrier spins and macrospin in an anisotropy field, and find a carrier mediated dephasing of the macrospin via mean-field

  6. Coupled nuclear spin relaxation and internal rotations in magnesium fluosilicate hexahydrate.

    NASA Technical Reports Server (NTRS)

    Utton, D. B.; Tsang, T.

    1972-01-01

    Both proton and fluorine nuclear spin-lattice relaxations have been studied by the 180- to 90-deg pulse method in magnesium fluosilicate hexahydrate at 25 and 13 MHz over the temperature range from 170 to 350 K. Observed nonexponential behavior of the nuclear magnetic relaxation is explained by internal rotations of the doubly charged negative fluosilicate ions and doubly charged positive magnesium hexahydrate ions.

  7. Properties of the low-spin high-spin interface during the relaxation of spin-crossover materials, investigated through an electro-elastic model

    SciTech Connect

    Slimani, A.; Boukheddaden, K. Varret, F.; Nishino, M.; Miyashita, S.

    2013-11-21

    The present work is devoted to the spatio-temporal investigations of spin-crossover lattices during their thermal relaxation from high- to low-spin state. The analysis is performed using Monte Carlo simulations on a distortable 2D lattice the sites of which are occupied by high-spin (HS) or low-spin (LS) atoms. The lattice is circular in shape and the HS to LS transformation results in single domain nucleation followed by growth and propagation processes. The evolution of the LS:HS interface is monitored during the relaxation process, through the mapping of spin states, displacement fields, local stresses, and elastic energy. The results show a curved interface, the curvature of which is reversed at the mid-transformation. The local stresses and elastic energy peak at the vicinity of the HS:LS interface, with sizeable dependence upon the position along the front line which evidences the edge effects.

  8. Spin-spin cross relaxation and spin-Hamiltonian spectroscopy by optical pumping of Pr/sup 3+/:LaF/sub 3/

    SciTech Connect

    Lukac, M.; Otto, F.W.; Hahn, E.L.

    1989-02-01

    We report the observation of an anticrossing in solid-state laser spectroscopy produced by cross relaxation. Spin-spin cross relaxation between the /sup 141/Pr- and /sup 19/F-spin reservoirs in Pr/sup 3+/:LaF/sub 3/ and its influence on the /sup 141/Pr NMR spectrum is detected by means of optical pumping. The technique employed combines optical pumping and hole burning with either external magnetic field sweep or rf resonance saturation in order to produce slow transient changes in resonant laser transmission. At a certain value of the external Zeeman field, where the energy-level splittings of Pr and F spins match, a level repulsion and discontinuity of the Pr/sup 3+/ NMR lines is observed. This effect is interpreted as the ''anticrossing'' of the combined Pr-F spin-spin reservoir energy states. The Zeeman-quadrupole-Hamiltonian spectrum of the hyperfine optical ground states of Pr/sup 3+/:LaF/sub 3/ is mapped out over a wide range of Zeeman magnetic fields. A new scheme is proposed for dynamic polarization of nuclei by means of optical pumping, based on resonant cross relaxation between rare spins and spin reservoirs.

  9. Spin Gap and Luttinger Liquid Description of the NMR Relaxation in Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Dóra, Balázs; Gulácsi, Miklós; Simon, Ferenc; Kuzmany, Hans

    2007-10-01

    Recent NMR experiments by Singer et al. [Singer , Phys. Rev. Lett. 95, 236403 (2005).PRLTAO0031-900710.1103/PhysRevLett.95.236403] showed a deviation from Fermi-liquid behavior in carbon nanotubes with an energy gap evident at low temperatures. Here, a comprehensive theory for the magnetic field and temperature dependent NMR C13 spin-lattice relaxation is given in the framework of the Tomonaga-Luttinger liquid. The low temperature properties are governed by a gapped relaxation due to a spin gap (˜30K), which crosses over smoothly to the Luttinger liquid behavior with increasing temperature.

  10. Spin relaxation in a hole-doped transition-metal dichalcogenide monolayer and bilayer with crystal defects

    NASA Astrophysics Data System (ADS)

    Habe, Tetsuro; Koshino, Mikito

    2016-02-01

    We study the electronic spin relaxation effect in the hole-doped monolayer and bilayer transition-metal dichalcogenide in the presence of the crystal defects. We consider realistic models of the lattice vacancy and actually estimate the spin relaxation rate using the multi-orbital tight-binding model. In the monolayer, the spin-relaxation time is found to be extremely long compared to the momentum relaxation time, and this is attributed to the fact that the spin hybridization in the band structure is suppressed by the mirror reflection symmetry. The bilayer TMD has a much shorter spin relaxation time in contrast, and this is attributed to stronger spin hybridization due to the absence of the mirror symmetry.

  11. Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents.

    PubMed

    Peat, David T; Horsewill, Anthony J; Köckenberger, Walter; Perez Linde, Angel J; Gadian, David G; Owers-Bradley, John R

    2013-05-28

    Many approaches are now available for achieving high levels of nuclear spin polarization. One of these methods is based on the notion that as the temperature is reduced, the equilibrium nuclear polarization will increase, according to the Boltzmann distribution. The main problem with this approach is the length of time it may take to approach thermal equilibrium at low temperatures, since nuclear relaxation times (characterized by the spin-lattice relaxation time T1) can become very long. Here, we show, by means of relaxation time measurements of frozen solutions, that selected lanthanide ions, in the form of their chelates with DTPA, can act as effective relaxation agents at low temperatures. Differential effects are seen with the different lanthanides that were tested, holmium and dysprosium showing highest relaxivity, while gadolinium is ineffective at temperatures of 20 K and below. These observations are consistent with the known electron-spin relaxation time characteristics of these lanthanides. The maximum relaxivity occurs at around 10 K for Ho-DTPA and 20 K for Dy-DTPA. Moreover, these two agents show only modest relaxivity at room temperature, and can thus be regarded as relaxation switches. We conclude that these agents can speed up solid state NMR experiments by reducing the T1 values of the relevant nuclei, and hence increasing the rate at which data can be acquired. They could also be of value in the context of a simple low-cost method of achieving several-hundred-fold improvements in polarization for experiments in which samples are pre-polarized at low temperatures, then rewarmed and dissolved immediately prior to analysis.

  12. NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning

    NASA Astrophysics Data System (ADS)

    Shmyreva, Anna A.; Safdari, Majid; Furó, István; Dvinskikh, Sergey V.

    2016-06-01

    Orders of magnitude decrease of 207Pb and 199Hg NMR longitudinal relaxation times T1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead(ii) halides, the most dramatic decrease of T1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200-15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

  13. NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning.

    PubMed

    Shmyreva, Anna A; Safdari, Majid; Furó, István; Dvinskikh, Sergey V

    2016-06-14

    Orders of magnitude decrease of (207)Pb and (199)Hg NMR longitudinal relaxation times T1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead(ii) halides, the most dramatic decrease of T1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200-15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

  14. Comparison of quantum and classical relaxation in spin dynamics.

    PubMed

    Wieser, R

    2013-04-01

    The classical Landau-Lifshitz equation with a damping term has been derived from the time evolution of a quantum mechanical wave function under the assumption of a non-Hermitian Hamilton operator. Further, the trajectory of a classical spin (S) has been compared with the expectation value of the spin operator (Ŝ). A good agreement between classical and quantum mechanical trajectories can be found for Hamiltonians linear in Ŝ or S, respectively. Quadratic or higher order terms in the Hamiltonian result in a disagreement.

  15. Hot-electron effect in spin relaxation of electrically injected electrons in intrinsic Germanium.

    PubMed

    Yu, T; Wu, M W

    2015-07-01

    The hot-electron effect in the spin relaxation of electrically injected electrons in intrinsic germanium is investigated by the kinetic spin Bloch equations both analytically and numerically. It is shown that in the weak-electric-field regime with E ≲ 0.5 kV cm(-1), our calculations have reasonable agreement with the recent transport experiment in the hot-electron spin-injection configuration (2013 Phys. Rev. Lett. 111 257204). We reveal that the spin relaxation is significantly enhanced at low temperature in the presence of weak electric field E ≲ 50 V cm(-1), which originates from the obvious center-of-mass drift effect due to the weak electron-phonon interaction, whereas the hot-electron effect is demonstrated to be less important. This can explain the discrepancy between the experimental observation and the previous theoretical calculation (2012 Phys. Rev. B 86 085202), which deviates from the experimental results by about two orders of magnitude at low temperature. It is further shown that in the strong-electric-field regime with 0.5 ≲ E ≲ 2 kV cm(-1), the spin relaxation is enhanced due to the hot-electron effect, whereas the drift effect is demonstrated to be marginal. Finally, we find that when 1.4 ≲ E ≲ 2 kV cm(-1) which lies in the strong-electric-field regime, a small fraction of electrons (≲5%) can be driven from the L to Γ valley, and the spin relaxation rates are the same for the Γ and L valleys in the intrinsic sample without impurity. With the negligible influence of the spin dynamics in the Γ valley to the whole system, the spin dynamics in the L valley can be measured from the Γ valley by the standard direct optical transition method.

  16. Matrix-assisted relaxation in Fe(phen)2(NCS)2 spin-crossover microparticles, experimental and theoretical investigations

    NASA Astrophysics Data System (ADS)

    Enachescu, Cristian; Tanasa, Radu; Stancu, Alexandru; Tissot, Antoine; Laisney, Jérôme; Boillot, Marie-Laure

    2016-07-01

    In this study, we present the influence of the embedding matrix on the relaxation of Fe(phen)2(NCS)2 (phen = 1,10-phenanthroline) spin-transition microparticles as revealed by experiments and provide an explanation within the framework of an elastic model based on a Monte-Carlo method. Experiments show that the shape of the high-spin → low-spin relaxation curves is drastically changed when the particles are dispersed in glycerol. This effect was considered in the model by means of interactions between the microparticles and the matrix. A faster start of the relaxation for microparticles embedded in glycerol is due to an initial positive local pressure acting on the edge spin-crossover molecules from the matrix side. This local pressure diminishes and eventually becomes negative during relaxation, as an effect of the decrease of the volume of spin-crossover microparticles from high-spin to low-spin.

  17. Multi-scales nuclear spin relaxation of liquids in porous media

    NASA Astrophysics Data System (ADS)

    Korb, Jean-Pierre

    2010-03-01

    The magnetic field dependence of the nuclear spin-lattice relaxation rate 1/T(ω) is a rich source of dynamical information for characterizing the molecular dynamics of liquids in confined environments. Varying the magnetic field changes the Larmor frequency ω, and thus the fluctuations to which the nuclear spin relaxation is sensitive. Moreover, this method permits a more complete characterization of the dynamics than the usual measurements as a function of temperature at fixed magnetic field strength, because many common solvent liquids have phase transitions that may alter significantly the character of the dynamics over the temperature range usually studied. Further, the magnetic field dependence of the spin-lattice relaxation rate, 1/T(ω), provides a good test of the theories that relate the measurement to the microdynamical behavior of the liquid. This is especially true in spatially confined systems where the effects of reduced dimensionality may force more frequent reencounters of the studied proton spin-bearing molecules with paramagnetic impurities at the pore surfaces that may alter the correlation functions that enter the relaxation equations in a fundamental way. We show by low field NMR relaxation that changing the amount of surface paramagnetic impurities leads to striking different pore-size dependences of the relaxation times T and T of liquids in pores. Here, we focus mainly on high surface area porous materials including calibrated porous silica glasses, granular packings, heterogeneous catalytic materials, cement-based materials and natural porous materials such as clay minerals and rocks. Recent highlights NMR relaxation works are reviewed for these porous materials, like continuous characterization of the evolving microstructure of various cementitious materials and measurement of wettability in reservoir carbonate rocks. Although, the recent applications of 2-dimensional T-T and T-z-store-T correlation experiments for characterization of

  18. Overcoming the low relaxivity of gadofosveset at high field with spin locking.

    PubMed

    Richardson, O C; Scott, M L J; Tanner, S F; Waterton, J C; Buckley, D L

    2012-10-01

    The contrast agent gadofosveset, which binds reversibly to serum albumin, has a high longitudinal relaxivity at lower magnetic fields (≤3.0 T) but a much lower relaxivity at high fields. Spin locking is sensitive to macromolecular content; it is hypothesized that combining this technique with the albumin-binding properties of gadofosveset may enable increased relaxivity at high fields. In vitro measurements at 4.7 T found significantly higher spin-lock relaxation rates, R1ρ (1/T1ρ), when gadofosveset was serum albumin-bound than when unbound. R1ρ values for a nonbinding contrast agent (gadopentetate dimeglumine) in serum albumin were similar to those for unbound gadofosveset. R2 (1/T2) values were also significantly higher at 4.7 T for serum albumin-bound gadofosveset than for unbound. Spin locking at high field generates significantly higher relaxation rates for gadofosveset than conventional contrast agents and may provide a method for differentiating free and bound molecules at these field strengths.

  19. General solution to gradient-induced transverse and longitudinal relaxation of spins undergoing restricted diffusion

    NASA Astrophysics Data System (ADS)

    Zheng, W.; Gao, H.; Liu, J.-G.; Zhang, Y.; Ye, Q.; Swank, C.

    2011-11-01

    We develop an approach, by calculating the autocorrelation function of spins, to derive the magnetic field gradient-induced transverse (T2) relaxation of spins undergoing restricted diffusion. This approach is an extension to the method adopted by McGregor. McGregor's approach solves the problem only in the fast diffusion limit; however, our approach yields a single analytical solution suitable in all diffusion regimes, including the intermediate regime. This establishes a direct connection between the well-known slow diffusion result of Torrey and the fast diffusion result. We also perform free induction decay measurements on spin-exchange optically polarized 3He gas with different diffusion constants. The measured transverse relaxation profiles are compared with the theory and satisfactory agreement has been found throughout all diffusion regimes. In addition to the transverse relaxation, this approach is also applicable to solving the longitudinal relaxation (T1) regardless of the diffusion limits. It turns out that the longitudinal relaxation in the slow diffusion limit differs by a factor of 2 from that in the fast diffusion limit.

  20. Partial lattice participation in the spin-lattice relaxation of potassium chromium alum

    NASA Astrophysics Data System (ADS)

    Overweg, J. A.; Flokstra, J.; ter Brake, H. J. M.; Gerritsma, G. J.

    1981-08-01

    We developed a SQUID-based frequency sweeping system for a.c. susceptibility measurements. Using this instrument we found that in Potassium Chromium Alum only a part of the lattice system is involved in the spin-lattice relaxation process. This partial lattice participation amounts 60-75% of the total lattice specific heat.

  1. Wide-band nanoscale magnetic resonance spectroscopy using quantum relaxation of a single spin in diamond

    NASA Astrophysics Data System (ADS)

    Wood, James D. A.; Broadway, David A.; Hall, Liam T.; Stacey, Alastair; Simpson, David A.; Tetienne, Jean-Philippe; Hollenberg, Lloyd C. L.

    2016-10-01

    We demonstrate an all-optical approach of nanoscale magnetic resonance (MR) spectroscopy whereby quantum relaxation (T1) of a single probe spin in diamond is monitored during a precise static magnetic field sweep to construct a spectrum of the surrounding spin environment. The method is inherently noninvasive as it involves no driving fields, and instead relies on the natural resonance between the quantum probe and target spins. As a proof of concept, we measure the T1-MR spectra across a wide band [megahertz (MHz) to gigahertz (GHz)] of a small ensemble of 14N impurities surrounding a single probe spin, providing information on both electron spin transitions (in the GHz range) and nuclear spin transitions (in the MHz range) of the 14N spin targets. Analysis of the T1-MR spectrum reveals that the electron spin transitions are probed via dipole interactions with the probe, while the relatively weak nuclear spin resonances are dramatically enhanced by hyperfine coupling in an electron-mediated process. With a projected sensitivity to external single-proton spins, this work establishes T1-MR as a powerful noninvasive wide-band technique for nanoscale MR spectroscopy.

  2. Knight shift and nuclear spin relaxation in Fe/n -GaAs heterostructures

    NASA Astrophysics Data System (ADS)

    Christie, K. D.; Geppert, C. C.; Patel, S. J.; Hu, Q. O.; Palmstrøm, C. J.; Crowell, P. A.

    2015-10-01

    We investigate the dynamically polarized nuclear spin system in Fe/n -GaAs heterostructures using the response of the electron-spin system to nuclear magnetic resonance (NMR) in lateral spin-valve devices. The hyperfine interaction is known to act more strongly on donor-bound electron states than on those in the conduction band. We provide a quantitative model of the temperature dependence of the occupation of donor sites. With this model we calculate the ratios of the hyperfine and quadrupolar nuclear relaxation rates of each isotope. For all temperatures measured, quadrupolar relaxation limits the spatial extent of nuclear spin polarization to within a Bohr radius of the donor sites and is directly responsible for the isotope dependence of the measured NMR signal amplitude. The hyperfine interaction is also responsible for the 2 kHz Knight shift of the nuclear resonance frequency that is measured as a function of the electron-spin accumulation. The Knight shift is shown to provide a measurement of the electron-spin polarization that agrees qualitatively with standard spin transport measurements.

  3. 1H nuclear spin relaxation of liquid water from molecular dynamics simulations.

    PubMed

    Calero, C; Martí, J; Guàrdia, E

    2015-02-01

    We have investigated the nuclear spin relaxation properties of (1)H in liquid water with the help of molecular dynamics simulations. We have computed the (1)H nuclear spin relaxation times T1 and T2 and determined the contribution of the different interactions to the relaxation at different temperatures and for different classical water models (SPC/E, TIP3P, TIP4P, and TIP4P/2005). Among the water models considered, the TIP4P/2005 model exhibits the best agreement with the experiment. The same analysis was performed with Car-Parrinello ab initio molecular dynamics simulations of bulk water at T = 330 K, which provided results close to the experimental values at room temperature. To complete the study, we have successfully accounted for the temperature-dependence of T1 and T2 in terms of a simplified model, which considers the reorientation in finite angle jumps and the diffusive translation of water molecules.

  4. Application to Rat Lung of the Extended Rorschach-Hazlewood Model of Spin-Lattice Relaxation

    NASA Astrophysics Data System (ADS)

    Hackmann, Andreas; Ailion, David C.; Ganesan, Krishnamurthy; Goodrich, K. Craig; Chen, Songhua; Laicher, Gernot; Cutillo, Antonio G.

    1996-02-01

    The spin-lattice relaxation timeT1was measured in excised degassed (airless) rat lungs over the frequency range 6.7 to 80.5 MHz. The observed frequency dependence was fitted successfully to the water-biopolymer cross-relaxation theory proposed by H. E. Rorschach and C. F. Hazlewood (RH) [J. Magn. Reson.70,79 (1986)]. The rotating frame spin-lattice relaxation timeT1ρwas also measured in rat lung fragments over the frequency range 0.56 to 5.6 kHz, and the observed frequency dependence was explained with an extension of the RH model. The agreement between the theory and the experimental data in both cases is good.

  5. Classical spin glass system in external field with taking into account relaxation effects

    SciTech Connect

    Gevorkyan, A. S. Abajyan, H. G.

    2013-08-15

    We study statistical properties of disordered spin systems under the influence of an external field with taking into account relaxation effects. For description of system the spatial 1D Heisenberg spin-glass Hamiltonian is used. In addition, we suppose that interactions occur between nearest-neighboring spins and they are random. Exact solutions which define angular configuration of the spin in nodes were obtained from the equations of stationary points of Hamiltonian and the corresponding conditions for the energy local minimum. On the basis of these recurrent solutions an effective parallel algorithm is developed for simulation of stabile spin-chains of an arbitrary length. It is shown that by way of an independent order of N{sup 2} numerical simulations (where N is number of spin in each chain) it is possible to generate ensemble of spin-chains, which is completely ergodic which is equivalent to full self-averaging of spin-chains' vector polarization. Distributions of different parameters (energy, average polarization by coordinates, and spin-spin interaction constant) of unperturbed system are calculated. In particular, analytically is proved and numerically is shown, that for the Heisenberg nearest-neighboring Hamiltonian model, the distribution of spin-spin interaction constants as opposed to widely used Gauss-Edwards-Anderson distribution satisfies Levy alpha-stable distribution law. This distribution is nonanalytic function and does not have variance. In the work we have in detail studied critical properties of an ensemble depending on value of external field parameters (from amplitude and frequency) and have shown that even at weak external fields the spin-glass systemis strongly frustrated. It is shown that frustrations have fractal behavior, they are selfsimilar and do not disappear at scale decreasing of area. By the numerical computation is shown that the average polarization of spin-glass on a different coordinates can have values which can lead to

  6. Electron spin echo of Cu(2+) in the triglycine sulfate crystal family (TGS, TGSe, TGFB): electron spin-lattice relaxation, Debye temperature and spin-phonon coupling.

    PubMed

    Lijewski, S; Goslar, J; Hoffmann, S K

    2006-07-01

    The electron spin-lattice relaxation of Cu(2+) has been studied by the electron spin echo technique in the temperature range 4.2-115 K in triglycine sulfate (TGS) family crystals. Assuming that the relaxation is due to Raman relaxation processes the Debye temperature Θ(D) was determined as 190 K for TGS, 168 K for triglycine selenate (TGSe) and 179 K for triglycine fluoroberyllate (TGFB). We also calculated the Θ(D) values from the sound velocities derived from available elastic constants. The elastic Debye temperatures were found as 348 K for TGS, 288 K for TGSe and 372 K for TGFB. The results shown good agreement with specific heat data for TGS. The elastic Θ(D) are considerably larger than those determined from the Raman spin-lattice relaxation. The possible reasons for this discrepancy are discussed. We propose to use a modified expression describing two-phonon Raman relaxation with a single variable only (Θ(D)) after elimination of the sound velocity. Moreover, we show that the relaxation data can be fitted using the elastic Debye temperature value as a constant with an additional relaxation process contributing at low temperatures. This mechanism can be related to a local mode of the Cu(2+) defect in the host lattice. Electron paramagnetic resonance g-factors and hyperfine splitting were analysed in terms of the molecular orbital theory and the d-orbital energies and covalency factors of the Cu(gly)(2) complexes were found. Using the structural data and calculated orbital energies the spin-phonon coupling matrix element of the second-order Raman process was calculated as 553 cm(-1) for TGS, 742 cm(-1) for TGSe and 569 cm(-1) for TGFB. PMID:21690828

  7. Spin dynamics and relaxation in the classical-spin Kondo-impurity model beyond the Landau-Lifschitz-Gilbert equation

    NASA Astrophysics Data System (ADS)

    Sayad, Mohammad; Potthoff, Michael

    2015-11-01

    The real-time dynamics of a classical spin in an external magnetic field and local exchange coupled to an extended one-dimensional system of non-interacting conduction electrons is studied numerically. Retardation effects in the coupled electron-spin dynamics are shown to be the source for the relaxation of the spin in the magnetic field. Total energy and spin is conserved in the non-adiabatic process. Approaching the new local ground state is therefore accompanied by the emission of dispersive wave packets of excitations carrying energy and spin and propagating through the lattice with Fermi velocity. While the spin dynamics in the regime of strong exchange coupling J is rather complex and governed by an emergent new time scale, the motion of the spin for weak J is regular and qualitatively well described by the Landau-Lifschitz-Gilbert (LLG) equation. Quantitatively, however, the full quantum-classical hybrid dynamics differs from the LLG approach. This is understood as a breakdown of weak-coupling perturbation theory in J in the course of time. Furthermore, it is shown that the concept of the Gilbert damping parameter is ill-defined for the case of a one-dimensional system.

  8. Muon Spin Relaxation Evidence for the U(1) Quantum Spin-Liquid Ground State in the Triangular Antiferromagnet YbMgGaO4

    NASA Astrophysics Data System (ADS)

    Li, Yuesheng; Adroja, Devashibhai; Biswas, Pabitra K.; Baker, Peter J.; Zhang, Qian; Liu, Juanjuan; Tsirlin, Alexander A.; Gegenwart, Philipp; Zhang, Qingming

    2016-08-01

    Muon spin relaxation (μ SR ) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO4 indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the μ+ spin relaxation rates, which are proportional to the dynamic correlation function of the Yb3 + spins, exhibit temperature-independent plateaus. All these μ SR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO4 .

  9. Muon Spin Relaxation Evidence for the U(1) Quantum Spin-Liquid Ground State in the Triangular Antiferromagnet YbMgGaO_{4}.

    PubMed

    Li, Yuesheng; Adroja, Devashibhai; Biswas, Pabitra K; Baker, Peter J; Zhang, Qian; Liu, Juanjuan; Tsirlin, Alexander A; Gegenwart, Philipp; Zhang, Qingming

    2016-08-26

    Muon spin relaxation (μSR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO_{4} indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the μ^{+} spin relaxation rates, which are proportional to the dynamic correlation function of the Yb^{3+} spins, exhibit temperature-independent plateaus. All these μSR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO_{4}. PMID:27610879

  10. Muon Spin Relaxation Evidence for the U(1) Quantum Spin-Liquid Ground State in the Triangular Antiferromagnet YbMgGaO_{4}.

    PubMed

    Li, Yuesheng; Adroja, Devashibhai; Biswas, Pabitra K; Baker, Peter J; Zhang, Qian; Liu, Juanjuan; Tsirlin, Alexander A; Gegenwart, Philipp; Zhang, Qingming

    2016-08-26

    Muon spin relaxation (μSR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO_{4} indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the μ^{+} spin relaxation rates, which are proportional to the dynamic correlation function of the Yb^{3+} spins, exhibit temperature-independent plateaus. All these μSR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO_{4}.

  11. Role of contact resistance in the effective spin relaxation rate in graphene spin valves

    NASA Astrophysics Data System (ADS)

    Stecklein, Gordon; Anugrah, Yoska; Li, Jing; Koester, Steven J.; Crowell, Paul

    Recent experiments (Maassen et al., PRB 86 235408 (2012), Idzuchi et al., PRB 91 241407(R) (2015)) have identified the role of finite contact resistances in determining the spin lifetime in graphene based on Hanle measurements of lateral spin valves. We have investigated this effect in spin valves fabricated using Co/AlOx tunnel barriers and graphene grown by chemical vapor deposition. By carrying out non-local spin valve and Hanle measurements over a wide range of gate voltages, we observe a variation in the spin signal that can be explained by the role of the contacts. Using the measured interface resistance, we quantify the degree of contact-induced spin sinking as the ratio of the contact resistance to the channel spin resistance and show that the variation in spin signal is explained by variation in this spin sinking parameter. By properly accounting for the effect of the contact resistance, we measure a spin lifetime that varies between 150-500 picoseconds. This work was supported by NSF ECCS-1124831, the NRI NEB program, and C-SPIN, a SRC STARNET center sponsored by MARCO and DARPA.

  12. Spin-lattice relaxation and the calculation of gain, pump power, and noise temperature in ruby

    NASA Technical Reports Server (NTRS)

    Lyons, J. R.

    1989-01-01

    The use of a quantitative analysis of the dominant source of relaxation in ruby spin systems to make predictions of key maser amplifier parameters is described. The spin-lattice Hamiltonian which describes the interaction of the electron spins with the thermal vibrations of the surrounding lattice is obtained from the literature. Taking into account the vibrational anisotropy of ruby, Fermi's rule is used to calculate the spin transition rates between the maser energy levels. The spin population rate equations are solved for the spin transition relaxation times, and a comparison with previous calculations is made. Predictions of ruby gain, inversion ratio, and noise temperature as a function of physical temperature are made for 8.4-GHz and 32-GHz maser pumping schemes. The theory predicts that ruby oriented at 90 deg will have approximately 50 percent higher gain in dB and slightly lower noise temperature than a 54.7-deg ruby at 32 GHz (assuming pump saturation). A specific calculation relating pump power to inversion ratio is given for a single channel of the 32-GHz reflected wave maser.

  13. Longitudinal spin relaxation of donor-bound electrons in direct band-gap semiconductors

    NASA Astrophysics Data System (ADS)

    Linpeng, Xiayu; Karin, Todd; Durnev, M. V.; Barbour, Russell; Glazov, M. M.; Sherman, E. Ya.; Watkins, S. P.; Seto, Satoru; Fu, Kai-Mei C.

    2016-09-01

    We measure the donor-bound electron longitudinal spin-relaxation time (T1) as a function of magnetic field (B ) in three high-purity direct band-gap semiconductors: GaAs, InP, and CdTe, observing a maximum T1 of 1.4, 0.4, and 1.2 ms, respectively. In GaAs and InP at low magnetic field, up to ˜2 T, the spin-relaxation mechanism is strongly density and temperature dependent and is attributed to the random precession of the electron spin in hyperfine fields caused by the lattice nuclear spins. In all three semiconductors at high magnetic field, we observe a power-law dependence T1∝B-ν with 3 ≲ν ≲4 . Our theory predicts that the direct spin-phonon interaction is important in all three materials in this regime in contrast to quantum dot structures. In addition, the "admixture" mechanism caused by Dresselhaus spin-orbit coupling combined with single-phonon processes has a comparable contribution in GaAs. We find excellent agreement between high-field theory and experiment for GaAs and CdTe with no free parameters, however a significant discrepancy exists for InP.

  14. Exchange bias training relaxation in spin glass/ferromagnet bilayers

    NASA Astrophysics Data System (ADS)

    Chi, Xiaodan; Rui, Wenbin; Du, Jun; Zhou, Shiming; Du, An; Hu, Yong

    2016-04-01

    A canonical spin glass (SG) FeAu layer is fabricated to couple to a soft ferromagnet (FM) FeNi layer. Below the SG freezing temperature, exchange bias (EB) and training are observed. Training in SG/FM bilayers is insensitive to cooling field and may suppress the EB or change the sign of the EB field from negative to positive at specific temperatures, violating from the simple power-law or the single exponential function derived from the antiferromagnet based systems. In view of the SG nature, we employ a double decay model to distinguish the contributions from the SG bulk and the SG/FM interface to training. Dynamical properties during training under different cooling fields and at different temperatures are discussed, and the nonzero shifting coefficient in the time index as a signature of slowing-down decay for SG based systems is interpreted by means of a modified Monte Carlo Metropolis algorithm.

  15. Estimating Bounds on Collisional Relaxation Rates of Spin-Polarized 87Rb Atoms at Ultracold Temperatures

    PubMed Central

    Mies, Frederick H.; Williams, Carl J.; Julienne, Paul S.; Krauss, Morris

    1996-01-01

    We present quantum scattering calculations for the collisional relaxation rate coefficient of spin-polarized 87Rb(f = 2,m = 2) atoms, which determines the loss rate of cold Rb atoms from a magnetic trap. Unlike the lighter alkali atoms, spin-polarized 87Rb atoms can undergo dipolar relaxation due to both the normal spin-spin dipole interaction and a second-order spin-orbit interaction with distant electronic states of the dimer. We present ab initio calculations for the second-order spin-orbit terms for both Rb2 and Cs2. The corrections lead to a reduction in the relaxation rate for 87Rb. Our primary concern is to analyze the sensitivity of the 87Rb trap loss to the uncertainties in the ground state molecular potentials. Since the scattering length for the a3Σ+u state is already known, the major uncertainties are associated with the X1Σ+g potential. After testing the effect of systematically modifying the short-range form of the molecular potentials over a reasonable range, and introducing our best estimate of the second-order spin-orbit interaction, we estimate that in the low temperature limit the rate coefficient for loss of Rb atoms from the f = 2,m = 2 state is between 0.4 × 10−15 cm3/s and 2.4 × 10−15 cm3/s (where this number counts two atoms lost per collision). In a pure condensate the rate coefficient would be reduced by 1/2.

  16. An approximate analytical expression for the nuclear quadrupole transverse relaxation rate of half-integer spins in liquids.

    PubMed

    Wu, Gang

    2016-08-01

    The nuclear quadrupole transverse relaxation process of half-integer spins in liquid samples is known to exhibit multi-exponential behaviors. Within the framework of Redfield's relaxation theory, exact analytical expressions for describing such a process exist only for spin-3/2 nuclei. As a result, analyses of nuclear quadrupole transverse relaxation data for half-integer quadrupolar nuclei with spin >3/2 must rely on numerical diagonalization of the Redfield relaxation matrix over the entire motional range. In this work we propose an approximate analytical expression that can be used to analyze nuclear quadrupole transverse relaxation data of any half-integer spin in liquids over the entire motional range. The proposed equation yields results that are in excellent agreement with the exact numerical calculations. PMID:27343483

  17. Spin and Time-Reversal Symmetries of Superconducting Electron Pairs Probed by the Muon Spin Rotation and Relaxation Technique

    NASA Astrophysics Data System (ADS)

    Higemoto, Wataru; Aoki, Yuji; MacLaughlin, Douglas E.

    2016-09-01

    Unconventional superconductivity based on the strong correlation of electrons is one of the central issues of solid-state physics. Although many experimental techniques are appropriate for investigating unconventional superconductivity, a complete perspective has not been established yet. The symmetries of electron pairs are crucial properties for understanding the essential state of unconventional superconductivity. In this review, we discuss the investigation of the time-reversal and spin symmetries of superconducting electron pairs using the muon spin rotation and relaxation technique. By detecting a spontaneous magnetic field under zero field and/or the temperature dependence of the muon Knight shift in the superconducting phase, the time-reversal symmetry and spin parity of electron pairs have been determined for several unconventional superconductors.

  18. Microviscosity of human erythrocytes studied using hypophosphite two-spin order relaxation.

    PubMed Central

    Price, W S; Perng, B C; Tsai, C L; Hwang, L P

    1992-01-01

    A new 31P NMR method is used to probe the cytoplasmic viscosity of human erythrocytes. The method is based on observing two-spin order relaxation of the 31P atom of the hypophosphite ion. This method is superior to our previous method, using the longitudinal relaxation time of the ion, because random field effects such as intermolecular dipole-dipole relaxation can be separated from intramolecular relaxation. This allows a more accurate determination of the effective reorientational correlation time from the measured intramolecular relaxation because it is now unaffected by random field effects. The new method also provides a means by which to estimate the random field effects. Both two-spin order and proton-decoupled T1 measurements were conducted on hypophosphite in water solutions at various temperatures, glycerol solutions of various viscosities, and in erythrocyte samples of various cell volumes. The results show that the effective reorientational correlation time of the hypophosphite ion varies from 7.2 to 15.2 ps in the cytoplasm of cells ranging in volume from 102 to 56 fl cells. PMID:1504239

  19. Deuterium off-resonance rotating frame spin-lattice relaxation of macromolecular bound ligands.

    PubMed Central

    Rydzewski, J M; Schleich, T

    1996-01-01

    Deuterated 3-trimethylsilylpropionic acid binding to bovine serum albumin was used as a model system to examine the feasibility and limitations of using the deuterium off-resonance rotating frame spin-lattice relaxation experiment for the study of equilibrium ligand-binding behavior to proteins. The results of this study demonstrate that the rotational-diffusion behavior of the bound species can be monitored directly, i.e., the observed correlation time of the ligand in the presence of a protein is approximately equal to the correlation time of the ligand in the bound state, provided that the fraction of bound ligand is at least 0.20. The presence of local ligand motion and/or chemical exchange contributions to relaxation in the bound state was inferred from the observation that the correlation time of the bound ligand was somewhat smaller than the correlation time characterizing the overall tumbling of the protein. An approximate value for the fraction of bound ligand was obtained from off-resonance relaxation experiments when supplemental spin-lattice or transverse relaxation times were employed in the analysis. Incorporation of local motion effects for the bound species into the theoretical relaxation formalism enabled the evaluation of an order parameter and an effective correlation time, which in conjunction with a wobbling in a cone model, provided additional information about ligand motion in the bound state. PMID:8785304

  20. Frequency dependence of electron spin-lattice relaxation for semiquinones in alcohol solutions

    NASA Astrophysics Data System (ADS)

    Elajaili, Hanan B.; Biller, Joshua R.; Eaton, Sandra S.; Eaton, Gareth R.

    2014-10-01

    The spin-lattice relaxation rates at 293 K for three anionic semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, and 2,3,5,6-tetramethoxy-1,4-benzosemiquinone) were studied at up to 8 frequencies between 250 MHz and 34 GHz in ethanol or methanol solution containing high concentrations of OH-. The relaxation rates are about a factor of 2 faster at lower frequencies than at 9 or 34 GHz. However, in perdeuterated alcohols the relaxation rates exhibit little frequency dependence, which demonstrates that the dominant frequency-dependent contribution to relaxation is modulation of dipolar interactions with solvent nuclei. The relaxation rates were modeled as the sum of two frequency-independent contributions (spin rotation and a local mode) and two frequency-dependent contributions (modulation of dipolar interaction with solvent nuclei and a much smaller contribution from modulation of g anisotropy). The correlation time for modulation of the interaction with solvent nuclei is longer than the tumbling correlation time of the semiquinone and is consistent with hydrogen bonding of the alcohol to the oxygen atoms of the semiquinones.

  1. /sup 1/H and /sup 13/C spin-lattice relaxation in gaseous benzene

    SciTech Connect

    Folkendt, M.M.; Weiss-Lopez, B.E.; True, N.S.

    1988-08-25

    The nuclear spin-lattice relaxation time, T/sub 1/, measured for benzene protons at densities between 0.81 and 54.4 mol/m/sup 3/ (15 and 980 Torr) at 381 K exhibits a characteristic nonlinear density dependence. Analysis of the density-dependent T/sub 1/ data yields a spin-rotation coupling constant, C/sub eff/, of /vert bar/182.6 (0.4)/vert bar/ Hz and an angular momentum reorientation cross section, sigma, of 131 (1) /Angstrom//sup 2/. The /sup 13/C spin-lattice relaxation time of singly labeled /sup 13/C benzene is a linear function of density over the density range 1.07-75.12 mol/m/sup 3/ (20-1330 Torr). /sup 13/C T/sub 1/ values are shorter than /sup 1/H T/sub 1/ values by a factor of ca. 100 at comparable densities. The nuclear Overhauser enhancement factor, /eta/, is 0.0 /plus minus/ 0.02 at densities between 11 and 85.3 mol/m/sup 3/ (200 and 1500 Torr), demonstrating that dipole-dipole relaxation is relatively inefficient in this region. The spin-rotation coupling constant, C/sub eff/, for /sup 13/C nuclei in benzene is estimated to be /vert bar/1602 (68)/vert bar/ Hz.

  2. Effects of spin diffusion on electron spin relaxation time measured with a time-resolved microscopic photoluminescence technique

    SciTech Connect

    Ikeda, Kazuhiro Kawaguchi, Hitoshi

    2015-02-07

    We performed measurements at room temperature for a GaAs/AlGaAs multiple quantum well grown on GaAs(110) using a time-resolved microscopic photoluminescence (micro-PL) technique to find what effects spin diffusion had on the measured electron spin relaxation time, τ{sub s}, and developed a method of estimating the spin diffusion coefficient, D{sub s}, using the measured data and the coupled drift-diffusion equations for spin polarized electrons. The spatial nonuniformities of τ{sub s} and the initial degree of electron spin polarization caused by the pump intensity distribution inside the focal spot were taken into account to explain the dependence of τ{sub s} on the measured spot size, i.e., a longer τ{sub s} for a smaller spot size. We estimated D{sub s} as ∼100 cm{sup 2}/s, which is similar to a value reported in the literature. We also provided a qualitative understanding on how spin diffusion lengthens τ{sub s} in micro-PL measurements.

  3. Rotating frame relaxation during adiabatic pulses versus conventional spin-lock: simulations and experimental results at 4T

    PubMed Central

    Mangia, Silvia; Liimatainen, Timo; Garwood, Michael; Michaeli, Shalom

    2009-01-01

    Spin relaxation taking place during radiofrequency (RF) irradiation can be assessed by measuring the longitudinal and transverse rotating frame relaxation rate constants (R1ρ and R2ρ). These relaxation parameters can be altered by utilizing different settings of the RF irradiation, thus providing a useful tool to generate contrast in MRI. In this work we investigate the dependencies of R1ρ and R2ρ due to dipolar interactions and anisochronous exchange (i.e., exchange between spins with different chemical shift δω≠0) on the properties of conventional spin-lock and adiabatic pulses, with particular emphasis on the latter ones which were not fully described previously. The results of simulations based on relaxation theory provide a foundation for formulating practical considerations for in vivo applications of rotating frame relaxation methods. Rotating frame relaxation measurements obtained from phantoms and from the human brain at 4T are presented to confirm the theoretical predictions. PMID:19559559

  4. An inversion-relaxation approach for sampling stationary points of spin model Hamiltonians

    NASA Astrophysics Data System (ADS)

    Hughes, Ciaran; Mehta, Dhagash; Wales, David J.

    2014-05-01

    Sampling the stationary points of a complicated potential energy landscape is a challenging problem. Here, we introduce a sampling method based on relaxation from stationary points of the highest index of the Hessian matrix. We illustrate how this approach can find all the stationary points for potentials or Hamiltonians bounded from above, which includes a large class of important spin models, and we show that it is far more efficient than previous methods. For potentials unbounded from above, the relaxation part of the method is still efficient in finding minima and transition states, which are usually the primary focus of attention for atomistic systems.

  5. /sup 13/C relaxation behavior in a coupled AMX spin system

    SciTech Connect

    Sterk, H.; Koenigsberger, E.

    1986-02-27

    The relaxation behavior of a coupled AMX spin system (cinnamic acid and methyl cinnamate) has been investigated. The description is based on the magnetization modes formalism proposed by Grant. The time evolution of the magnetization, which determines the relaxation behavior, is measured via inversion recovery experiments. The diffusion constants as well as the random fields are fitted by means of a least-squares procedure. To gain verification for these values a cross-check with different independent measurements as well as calculations based on the frictional description of the molecules has been employed. 16 references, 2 figures, 4 tables.

  6. Nuclear magnetic relaxation by the dipolar EMOR mechanism: General theory with applications to two-spin systems.

    PubMed

    Chang, Zhiwei; Halle, Bertil

    2016-02-28

    In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. We have embarked on a systematic program to develop, from the stochastic Liouville equation, a general and rigorous theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole coupling strengths, and Larmor frequencies. Here, we present a general theoretical framework applicable to spin systems of arbitrary size with symmetric or asymmetric exchange. So far, the dipolar EMOR theory is only available for a two-spin system with symmetric exchange. Asymmetric exchange, when the spin system is fragmented by the exchange, introduces new and unexpected phenomena. Notably, the anisotropic dipole couplings of non-exchanging spins break the axial symmetry in spin Liouville space, thereby opening up new relaxation channels in the locally anisotropic sites, including longitudinal-transverse cross relaxation. Such cross-mode relaxation operates only at low fields; at higher fields it becomes nonsecular, leading to an unusual inverted relaxation dispersion that splits the extreme-narrowing regime into two sub-regimes. The general dipolar EMOR theory is illustrated here by a detailed analysis of the asymmetric two-spin case, for which we present relaxation dispersion profiles over a wide range of conditions as well as analytical results for integral relaxation rates and time-dependent spin modes in the zero-field and motional-narrowing regimes. The general theoretical framework presented here will enable a quantitative analysis of frequency-dependent water-proton longitudinal relaxation in model systems with immobilized macromolecules and, ultimately, will provide a rigorous link between relaxation-based magnetic resonance image contrast and molecular parameters

  7. Observation of the vortex lattice melting by NMR spin-lattice relaxation in the mixed state

    SciTech Connect

    Bulaevskii, L.N.; Hammel, P.C.; Vinokur, V.M.

    1994-01-01

    For anisotropic layered superconductors the effect of moving vortices on the nuclear spin magnetization is calculated. Current is supposed to flow along layers, and applied magnetic field is tilted with respect to c-axis. In the solid phase the motion of the vortex lattice produces an alternating magnetic field perpendicular to the applied field which causes the decay of the spin-echo amplitude. This decay rate will display an array of peaks as a function of frequency. In the liquid phase this alternating field contribute to the longitudinal relaxation rate W{sub 1} which has a single peak.

  8. Suppression of Raman electron spin relaxation of radicals in crystals. Comparison of Cu2+ and free radical relaxation in triglycine sulfate and Tutton salt single crystals.

    PubMed

    Hoffmann, S K; Goslar, J; Lijewski, S

    2011-08-31

    Electron spin-lattice relaxation was measured by the electron spin echo method in a broad temperature range above 4.2 K for Cu(2+) ions and free radicals produced by ionizing radiation in triglycine sulfate (TGS) and Tutton salt (NH4)(2)Zn(SO4)2 ⋅ 6H2O crystals. Localization of the paramagnetic centres in the crystal unit cells was determined from continuous wave electron paramagnetic resonance spectra. Various spin relaxation processes and mechanisms are outlined. Cu(2+) ions relax fast via two-phonon Raman processes in both crystals involving the whole phonon spectrum of the host lattice. This relaxation is slightly slower for TGS where Cu(2+) ions are in the interstitial position. The ordinary Raman processes do not contribute to the radical relaxation which relaxes via the local phonon mode. The local mode lies within the acoustic phonon band for radicals in TGS but within the optical phonon range in (NH4)(2)Zn(SO4)2 ⋅ 6H2O. In the latter the cross-relaxation was considered. A lack of phonons around the radical molecules suggested a local crystal amorphisation produced by x- or γ-rays.

  9. Nuclear-spin relaxation of ²º⁷Pb in ferroelectric powders

    SciTech Connect

    Bouchard, Louis S.; Sushkov, Alexander O.; Budker, Dmitry; Ford, Joe; Lipton, Andrew S.

    2008-02-05

    The ²º⁷Pb nuclear system (nuclear spin I = 1/2; magnetic Moment μ ≈0.58 μN; isotopic abundance ≈ 22%) in ferroelectric solids has been proposed for a search for a Schiff moment associated with simultaneous violation of parity (P) and time-reversal invariance (T) in fundamental interactions [1] (see also a discussion of the sensitivity of such search in Ref. [2]). The idea is that, due to the Schiff moment, a ferroelectric sample would acquire a P,T-odd magnetic polarization along the direction of its electric polarization. In conclusion, we have presented the first experimental study of relaxation properties of ²º⁷Pb in PT and PZT below room temperature. We find that above T≈ 50 K, longitudinal relaxation rate follows the T² dependence characteristic of the two-phonon Raman process. On the other hand, as the temperature is decreased below T≈ 50 K, the longitudinal relaxation rates drop slower than ∝T2 (as opposed to ∝T7 expected for the Raman process), and the relaxation is probably due to a direct process associated with paramagnetic impurities and nuclear-spin diffusion. While the longitudinal relaxation times T₁ vary between several seconds and over an hour in the temperature range between 290 and 10 K, the transverse relaxation time T₂ is found to be ≈1.5 ms for all temperatures and all powder samples studied. D: we never discuss the origin of T₂ relaxation. Maybe we should. 1.5 ms is only a bit shorter from what would be expected from nuclear spin-spin interactions. Any comments? At some point Sasha asked Oleg to calculate T₂ exactly for PT and PZT, but I forgot what was the result. If such calculation exists, it would be great to compare with the expt. result. The obtained results provide an important input in the design of the experiments to search for P,T-violating effects in solid ferroelectrics

  10. Structural aspects of the relaxation process in spin crossover solids: Phase separation, mapping of lattice strain, and domain wall structure

    NASA Astrophysics Data System (ADS)

    Nicolazzi, W.; Pillet, S.

    2012-03-01

    We present a nonequilibrium study of the relaxation process in spin crossover solids using numerical simulations of a recently introduced two-variable elastic Ising-like model. We analyze the structural lattice distortions accompanying the relaxation from the metastable high-spin to the ground low-spin state as a function of cooperativity. In the highly cooperative case, a sigmoidal relaxation behavior of the high-spin fraction nHS is described, and it occurs jointly with a structural phase separation process. The mean lattice spacing follows a similar sigmoidal trend, owing to the interplay between electronic and lattice variables in the Hamiltonian. Weakly cooperative systems are characterized by single exponential relaxations of the high-spin fraction, the corresponding structural transformation proceeds homogeneously with a progressive relaxation of the mean lattice spacing. Long relaxation tail effects are also observed. We highlight the development of lattice strain accompanying the spin transition, and show that structural phase rebuilding proceeds in the late stage of the relaxation by releasing residual strain. Under specific conditions, a temporal decoupling between the electronic and lattice variables is observed, which may have direct applications for interpreting time-resolved spectroscopic or diffraction experiments and for elucidating unusual structural behaviors, such as the development of superstructures, modulated structures, or transient phases.

  11. Polarized Alkali-Metal Vapor with Minute-Long Transverse Spin-Relaxation Time

    NASA Astrophysics Data System (ADS)

    Balabas, M. V.; Karaulanov, T.; Ledbetter, M. P.; Budker, D.

    2010-08-01

    We demonstrate lifetimes of Zeeman populations and coherences in excess of 60 sec in alkali-metal vapor cells with inner walls coated with an alkene material. This represents 2 orders of magnitude improvement over the best paraffin coatings. We explore the temperature dependence of cells coated with this material and investigate spin-exchange relaxation-free magnetometry in a room-temperature environment, a regime previously inaccessible with conventional coating materials.

  12. Electron spin relaxation of C60 monoanion in liquid solution: applicability of Kivelson-Orbach mechanism.

    PubMed

    Kundu, Krishnendu; Kattnig, Daniel R; Mladenova, Boryana; Grampp, Günter; Das, Ranjan

    2015-04-01

    We report the results of our investigation on the electron spin relaxation mechanism of the monoanion of C60 fullerene in liquid solution. The solvent chosen was carbon disulfide, which is rather uncommon in EPR spectroscopy but proved very useful here because of its liquid state over a wide temperature range. The conditions for exclusive formation of the monoanion of C60 in CS2 were first determined using electrochemical measurements. Using these results, only the monoanion of C60 was prepared by chemical reduction using Hg2I2/Hg as the reducing agent. The EPR line width was measured over a wide temperature range of 120-290 K. The line widths show weak dependence on temperature, changing by a factor of only about 2, over this temperature range. We show that the observed temperature dependence does not obey the Kivelson-Orbach mechanism of electron spin relaxation in liquids, applicable for radicals with low-lying, thermally accessible excited electronic states. The observed temperature dependence can be empirically fitted to an Arrhenius type of exponential function, from which an activation energy of 74 ± 3 cm(-1) is obtained. From the qualitative similarities in the characteristics of the spin relaxation rates of C60 monoanion radical and the cyclohexane type of cation radicals reported in the literature, we propose that a pseudorotation-induced electron spin relaxation process could be operating in the C60 monoanion radical in liquid solution. The low activation energy of 74 cm(-1) observed here is consistent with the pseudorotation barrier of C60 monoanion, estimated from reported Jahn-Teller energy levels. PMID:25789609

  13. 19F nuclear spin relaxation and spin diffusion effects in the single-ion magnet LiYF4:Ho3+

    NASA Astrophysics Data System (ADS)

    Malkin, B. Z.; Vanyunin, M. V.; Graf, M. J.; Lago, J.; Borsa, F.; Lascialfari, A.; Tkachuk, A. M.; Barbara, B.

    2008-11-01

    Temperature and magnetic field dependences of the 19F nuclear spin-lattice relaxation in a single crystal of LiYF4 doped with holmium are described by an approach based on a detailed consideration of the magnetic dipole-dipole interactions between nuclei and impurity paramagnetic ions and nuclear spin diffusion processes. The observed non-exponential long time recovery of the nuclear magnetization after saturation at intermediate temperatures is in agreement with predictions of the spin-diffusion theory in a case of the diffusion limited relaxation. At avoided level crossings in the spectrum of electron-nuclear states of Ho3 + ions, rates of nuclear spin-lattice relaxation increase due to quasi-resonant energy exchange between nuclei and paramagnetic ions in contrast to the predominant role played by electronic cross-relaxation processes in the low-frequency ac-susceptibility.

  14. Ion distribution in copper exchanged zeolites by using Si-29 spin lattice relaxation analysis

    NASA Astrophysics Data System (ADS)

    Palamara, Joseph; Seidel, Karsten; Moini, Ahmad; Prasad, Subramanian

    2016-06-01

    Transition metal-containing zeolites, particularly those with smaller pore size, have found extensive application in the selective catalytic reduction (SCR) of environmental pollutants containing nitrogen oxides. We report these zeolites have dramatically faster silicon-29 (Si-29) spin lattice relaxation times (T1) compared to their sodium-containing counterparts. Paramagnetic doping allows one to acquire Si-29 MAS spectra in the order of tens of seconds without significantly affecting the spectral resolution. Moreover, relaxation times depend on the method of preparation and the next-nearest neighbor silicon Qn(mAl) sites, where n = 4 and m = 0-4, respectively. A clear trend is noted between the effectiveness of Cu exchange and the Si-29 NMR relaxation times. It is anticipated that the availability of this tool, and the enhanced understanding of the nature of the active sites, will provide the means for designing improved SCR catalysts.

  15. Ion distribution in copper exchanged zeolites by using Si-29 spin lattice relaxation analysis.

    PubMed

    Palamara, Joseph; Seidel, Karsten; Moini, Ahmad; Prasad, Subramanian

    2016-06-01

    Transition metal-containing zeolites, particularly those with smaller pore size, have found extensive application in the selective catalytic reduction (SCR) of environmental pollutants containing nitrogen oxides. We report these zeolites have dramatically faster silicon-29 (Si-29) spin lattice relaxation times (T1) compared to their sodium-containing counterparts. Paramagnetic doping allows one to acquire Si-29 MAS spectra in the order of tens of seconds without significantly affecting the spectral resolution. Moreover, relaxation times depend on the method of preparation and the next-nearest neighbor silicon Qn(mAl) sites, where n=4 and m=0-4, respectively. A clear trend is noted between the effectiveness of Cu exchange and the Si-29 NMR relaxation times. It is anticipated that the availability of this tool, and the enhanced understanding of the nature of the active sites, will provide the means for designing improved SCR catalysts. PMID:27055207

  16. Merging of the α and β relaxations in polybutadiene: A neutron spin echo and dielectric study

    NASA Astrophysics Data System (ADS)

    Arbe, A.; Richter, D.; Colmenero, J.; Farago, B.

    1996-10-01

    The local dynamics of 1,4 polybutadiene below and above the merging of the α and β relaxations have been investigated by combining neutron spin echo (NSE) and dielectric spectroscopy. The study of the dynamic structure factor measured by NSE over a wide momentum transfer range allows us to characterize the α relaxation as an interchain process while the β relaxation originates from mainly intrachain motions. At temperatures below the merging, the dynamic structure factor can be described by a superposition of elemental processes for the β relaxation as obtained from dielectric spectroscopy. The elemental motions behind this process can be related to rotational jumps of the chain building blocks around their center of mass. Furthermore, we have been able to consistently describe the dynamic structure factor above the merging of the α and β relaxations by assuming that both processes are statistically independent. In the framework of this scenario a procedure for analyzing the dielectric response in the α-β merging region has been developed. Its application to the dielectric data allows us to describe the dielectric response in this region on the basis of the low temperature behavior of the α and β processes and without considering any particular change in the relaxation mechanism of these processes. The temperature dependence found for the relaxation time of the α process follows now the viscosity, a masked feature in the experimental data due to the merging process. In this way, we have been able to consistently describe the relaxation of both, the polarization and the density fluctuations, by using the same scenario, i.e., independent α and β processes, and considering the same functional forms and temperature dependences of the characteristic times of the two processes.

  17. Electron spin relaxation time in (110) InGaAs/InAlAs quantum wells

    SciTech Connect

    Yokota, Nobuhide; Yasuda, Yusuke; Ikeda, Kazuhiro; Kawaguchi, Hitoshi

    2014-07-14

    Electron spin relaxation time τ{sub s} in InGaAs/InAlAs quantum wells (QWs) grown on (110) and (100) InP substrates was investigated by pump-probe transmission measurements. Similar τ{sub s} of 0.83–1.0 ns were measured at room temperature for all the measured (110) and (100) QWs, indicating suppression of the D'yakonov-Perel' spin relaxation mechanism in (110) QWs is not effective in InGaAs/InAlAs QWs as opposed to GaAs/AlGaAs QWs. Contribution of the Bir-Aronov-Pikus mechanism dominant in (110) GaAs/AlGaAs QWs was found to be small in both the (110) and (100) InGaAs/InAlAs QWs from the weak dependences of τ{sub s} on pump intensity at room temperature. These results suggest that the spin relaxation mechanism dominant in InGaAs/InAlAs QWs at a temperature higher than 200 K is the Elliott-Yafet mechanism independent of the crystal orientation among the above three major mechanisms.

  18. Magnetic field dependence of muon spin relaxation in geometrically frustrated Gd2Ti2O7

    NASA Astrophysics Data System (ADS)

    Dunsiger, S. R.; Kiefl, R. F.; Chakhalian, J. A.; Greedan, J. E.; Macfarlane, W. A.; Miller, R. I.; Morris, G. D.; Price, A. N.; Raju, N. P.; Sonier, J. E.

    2006-05-01

    Muon spin relaxation has been investigated in the geometrically frustrated antiferromagnet Gd2Ti2O7 as a function of magnetic field and temperature. Well above the magnetic ordering temperature of Tc=1K , the field dependence of the muon spin relaxation rate (T1-1) originates from field-induced changes in the spectral density of Gd fluctuations. This allows one to determine both the autocorrelation time and magnitude of the fluctuating local magnetic field at the muon. Well below Tc a coherent precession signal is observed, corresponding to a much smaller quasistatic local magnetic field. At low temperatures T1-1 levels off, at a constant value which is much larger than reported recently for a single crystal of Gd2Ti2O7 [Yaouanc , Phys. Rev. Lett. 95, 047203 (2005)]. A magnetic field of 2T completely quenches the low-temperature spin relaxation in the present sample. These results indicate that the ordered state is characterized by low-frequency dynamics which are most likely due to residual crystalline disorder.

  19. Effect of glassy modes on electron spin-lattice relaxation in solid ethanol

    NASA Astrophysics Data System (ADS)

    Merunka, Dalibor; Kveder, Marina; Jokić, Milan; Rakvin, Boris

    2013-03-01

    Electron spin-lattice relaxation (SLR) of TEMPO radical was measured in the crystalline and glassy states of deuterated ethanol in the temperature range 5-80 K using X-band electron paramagnetic resonance (EPR). The measured SLR rates are higher in the glassy than in crystalline state and the excess SLR rate in glassy state is much lower than in ethanol. This result suggests that extra modes in glassy state, i.e. glassy modes, produce the excess SLR rate via the electron-nuclear dipolar (END) interaction between the electron spin of radical and the matrix protons or deuterons. Using the soft-potential model and assuming the END interaction between the electron spin and the matrix protons, the contributions to SLR rate of various mechanisms of glassy modes were theoretically analyzed. The evaluations of SLR rates in glassy ethanol indicate two main mechanisms of glassy modes: thermally activated relaxation of double-well systems and phonon-induced relaxation of quasi-harmonic local modes. The SLR rates induced by these mechanisms correlate well with the experimental data.

  20. Spin relaxation of radicals in cryptochrome and its role in avian magnetoreception.

    PubMed

    Worster, Susannah; Kattnig, Daniel R; Hore, P J

    2016-07-21

    Long-lived spin coherence and rotationally ordered radical pairs have previously been identified as key requirements for the radical pair mechanism of the avian magnetic compass sense. Both criteria are hard to meet in a biological environment, where thermal motion of the radicals creates dynamic disorder and drives efficient spin relaxation. This has long been cited as a major stumbling block of the radical pair hypothesis. Here we combine Redfield relaxation theory with analytical solutions to a rotational diffusion equation to assess the impact of restricted rotational motion of the radicals on the operation of the compass. The effects of such motions are first investigated generally in small, model systems and are then critically examined in the magnetically sensitive flavin-tryptophan radical pair that is formed photochemically in the proposed magnetoreceptor protein, cryptochrome. We conclude that relaxation is slowest when rotational motion of the radicals within the protein is fast and highly constrained; that in a regime of slow relaxation, the motional averaging of hyperfine interactions has the potential to improve the sensitivity of the compass; and that consideration of motional effects can significantly alter the design criteria for an optimal compass. In addition, we demonstrate that motion of the flavin radical is likely to be compatible with its role as a component of a functioning radical-pair compass, whereas the motion of the tryptophan radical is less ideal, unless it is particularly fast. PMID:27448908

  1. Spin relaxation of radicals in cryptochrome and its role in avian magnetoreception

    NASA Astrophysics Data System (ADS)

    Worster, Susannah; Kattnig, Daniel R.; Hore, P. J.

    2016-07-01

    Long-lived spin coherence and rotationally ordered radical pairs have previously been identified as key requirements for the radical pair mechanism of the avian magnetic compass sense. Both criteria are hard to meet in a biological environment, where thermal motion of the radicals creates dynamic disorder and drives efficient spin relaxation. This has long been cited as a major stumbling block of the radical pair hypothesis. Here we combine Redfield relaxation theory with analytical solutions to a rotational diffusion equation to assess the impact of restricted rotational motion of the radicals on the operation of the compass. The effects of such motions are first investigated generally in small, model systems and are then critically examined in the magnetically sensitive flavin-tryptophan radical pair that is formed photochemically in the proposed magnetoreceptor protein, cryptochrome. We conclude that relaxation is slowest when rotational motion of the radicals within the protein is fast and highly constrained; that in a regime of slow relaxation, the motional averaging of hyperfine interactions has the potential to improve the sensitivity of the compass; and that consideration of motional effects can significantly alter the design criteria for an optimal compass. In addition, we demonstrate that motion of the flavin radical is likely to be compatible with its role as a component of a functioning radical-pair compass, whereas the motion of the tryptophan radical is less ideal, unless it is particularly fast.

  2. Nuclear spin relaxation of {sup 129}Xe due to persistent xenon dimers

    SciTech Connect

    Berry-Pusey, B. N.; Anger, B. C.; Laicher, G.; Saam, B.

    2006-12-15

    We have measured longitudinal nuclear relaxation rates of {sup 129}Xe in Xe-N{sub 2} mixtures at densities below 0.5 amagats in a magnetic field of 8.0 T. We find that intrinsic spin relaxation in this regime is principally due to fluctuations in the intramolecular spin-rotation (SR) and chemical-shift-anisotropy (CSA) interactions, mediated by the formation of {sup 129}Xe-Xe persistent dimers. Our results are consistent with previous work done in one case at much lower applied fields where the CSA interaction is negligible and in another case at much higher gas densities where transient xenon dimers mediate the interactions. We have verified that a large applied field suppresses the persistent-dimer mechanism, consistent with standard relaxation theory, allowing us to measure room-temperature gas-phase relaxation times T{sub 1} for {sup 129}Xe greater than 25 h at 8.0 T. These data also yield a maximum possible low-field T{sub 1} for pure xenon gas at room temperature of 5.45{+-}0.2 h. The coupling strengths for the SR and CSA interactions that we extract are in fair agreement with estimates based both on previous experimental work and on ab initio calculations. Our results have potential implications for the production and storage of large quantities of hyperpolarized {sup 129}Xe for use in various applications.

  3. Investigation of wettability by NMR microscopy and spin-lattice relaxation

    SciTech Connect

    Doughty, D.A.; Tomutsa, Liviu

    1993-11-01

    The wettability of reservoir rock has an important impact on the efficiency of oil recovery processes and the distribution of oil and water within the reservoir. One of the potentially useful tools for wettability measurements is nuclear magnetic resonance (NMR) and spin-lattice relaxation. More recently using NMR microscopy NIPER has developed the capability of imaging one- and two-phase fluid systems in reservoir rock at resolutions to 25 microns. Effects seen in the images of fluids within the pore space of rocks near the rock grain surfaces hinted at the possibility of using NMR microscopy to map the wettability variations at grain sites within the pore space. Investigations were begun using NMR microscopy and spin-lattice relaxation time measurements on rock/fluid systems and on well-defined fractional wet model systems to study these effects. Relaxation data has been modelled using the stretched exponential relationship recently introduced. Comparisons of the NMR microscopy results of the model system with the rock results indicate that the observed effects probably do not reflect actual wettability variations within the pore space. The results of the relaxation time measurements reveal that even in the simple model studied, the behavior of two phases is somewhat ambiguous and much more complex and requires more study.

  4. Spin-lattice relaxation via quantum tunneling in diluted crystals of Fe4 single-molecule magnets

    NASA Astrophysics Data System (ADS)

    Repollés, A.; Cornia, A.; Luis, F.

    2014-02-01

    We investigate the dynamic susceptibility of Fe4 single-molecule magnets with integer spin (S =5) in the form of pure crystals as well as diluted in crystals of isostructural, but nonmagnetic, Ga4 clusters. Below approximately 1 K, the spin-lattice relaxation becomes dominated by a temperature-independent process. The spin-lattice relaxation time τ measured in this "quantum regime" is 12 orders of magnitude shorter than the characteristic time scale of direct phonon-induced processes but agrees with the relaxation times of pure (i.e., not assisted by phonons) spin tunneling events. The present results show that the latter phenomenon, despite conserving the energy of the ensemble of electronic and nuclear spins, drives the thermalization of electronic spins at very low temperatures. The spin-lattice relaxation time scales with the concentration of Fe4, thus suggesting that the main effect of dipolar interactions is to block tunneling. The data show therefore no evidence for the contribution of collective phonon emission processes, such as phonon superradiance, to the spin-lattice relaxation.

  5. 1H-13C/1H-15N Heteronuclear Dipolar Recoupling by R-Symmetry Sequences Under Fast Magic Angle Spinning for Dynamics Analysis of Biological and Organic Solids

    PubMed Central

    Hou, Guangjin; Byeon, In-Ja L.; Ahn, Jinwoo; Gronenborn, Angela M.; Polenova, Tatyana

    2011-01-01

    Fast magic angle spinning (MAS) NMR spectroscopy is becoming increasingly important in structural and dynamics studies of biological systems and inorganic materials. Superior spectral resolution due to the efficient averaging of the dipolar couplings can be attained at MAS frequencies of 40 kHz and higher with appropriate decoupling techniques, while proton detection gives rise to significant sensitivity gains, therefore making fast MAS conditions advantageous across the board compared with the conventional slow- and moderate-MAS approaches. At the same time, many of the dipolar recoupling approaches that currently constitute the basis for structural and dynamics studies of solid materials and that are designed for MAS frequencies of 20 kHz and below, fail above 30 kHz. In this report, we present an approach for 1H-13C/1H-15N heteronuclear dipolar recoupling under fast MAS conditions using R-type symmetry sequences, which is suitable even for fully protonated systems. A series of rotor-synchronized R-type symmetry pulse schemes are explored for the determination of structure and dynamics in biological and organic systems. The investigations of the performance of the various RNnv-symmetry sequences at the MAS frequency of 40 kHz experimentally and by numerical simulations on [U-13C,15N]-alanine and [U-13C,15N]-N-acetyl-valine, revealed excellent performance for sequences with high symmetry number ratio (N/2n > 2.5). Further applications of this approach are presented for two proteins, sparsely 13C/uniformly 15N enriched CAP-Gly domain of dynactin and U-13C,15N-Tyr enriched C-terminal domain of HIV-1 CA protein. 2D and 3D R1632-based DIPSHIFT experiments carried out at the MAS frequency of 40 kHz, yielded site-specific 1H-13C/1H-15N heteronuclear dipolar coupling constants for CAP-Gly and CTD CA, reporting on the dynamic behavior of these proteins on time scales of nano- to microseconds. The R-symmetry based dipolar recoupling under fast MAS is expected to find

  6. The Search for Magnetic Order in delta-Pu metal using muon spin relaxation

    SciTech Connect

    Heffner, R; Ohishi, K; Fluss, M; Morris, G; MacLaughlin, D; Shu, L; Chung, B; McCall, S; Bauer, E; Sarrao, J; Ito, T; Higemoto, W

    2006-10-16

    We review results from previous muon spin relaxation ({mu}SR) measurements in applied fields of H{sub 0} = 0 and 0.25 T which established an upper limit for the ordered or disordered frozen spin moment above T = 4 K in {delta}-Pu (4.3 at. % Ga) of {micro}{sub ord} {le} 10{sup -3} {mu}{sub B}. In addition, we present new data in H{sub 0} = 0.25 T and 2 T applied field on a highly annealed {delta}-Pu (4.3 at. % Ga) sample. Neither the muon Knight shift (H{sub 0} = 2 T) nor the inhomogeneous linewidths in the new sample show appreciable temperature dependence below about T = 60 K, also consistent with no spin freezing. Recent theoretical arguments advanced to explain these results are mentioned.

  7. Spin relaxation and donor-acceptor recombination of Se+ in 28-silicon

    NASA Astrophysics Data System (ADS)

    Lo Nardo, Roberto; Wolfowicz, Gary; Simmons, Stephanie; Tyryshkin, Alexei M.; Riemann, Helge; Abrosimov, Nikolai V.; Becker, Peter; Pohl, Hans-Joachim; Steger, Michael; Lyon, Stephen A.; Thewalt, Mike L. W.; Morton, John J. L.

    2015-10-01

    Selenium impurities in silicon are deep double donors and their optical and electronic properties have been recently investigated due to their application for infrared detection. However, a singly ionized selenium donor (Se+) possesses an electron spin which makes it a potential candidate as a silicon-based spin qubit, with significant potential advantages compared to the more commonly studied group V donors. Here we study the electron spin relaxation (T1) and coherence (T2) times of Se+ in isotopically purified 28-silicon, and find them to be up to two orders of magnitude longer than shallow group V donors at temperatures above ˜15 K . We further study the dynamics of donor-acceptor recombination between selenium and boron, demonstrating that it is possible to control the donor charge state through optical excitation of neutral Se0.

  8. Hysteresis of noninteracting and spin-orbit-coupled atomic Fermi gases with relaxation

    NASA Astrophysics Data System (ADS)

    Metcalf, Mekena; Lai, Chen-Yen; Chien, Chih-Chun

    2016-05-01

    Hysteresis can be found in driven many-body systems such as magnets and superfluids. Rate-dependent hysteresis arises when a system is driven periodically while relaxing towards equilibrium. A two-state paramagnet driven by an oscillating magnetic field in the relaxation approximation clearly demonstrates rate-dependent hysteresis. A noninteracting atomic Fermi gas in an optical ring potential, when driven by a periodic artificial gauge field and subjected to dissipation, is shown to exhibit hysteresis loops of atomic current due to a competition of the driving time and the relaxation time. This is in contrast to electronic systems exhibiting equilibrium persistent current driven by magnetic flux due to rapid relaxation. Universal behavior of the dissipated energy in one hysteresis loop is observed in both magnetic and atomic systems, showing linear and inverse-linear dependence on the relaxation time in the strong and weak dissipation regimes. While interactions in general invalidate the framework for rate-dependent hysteresis, an atomic Fermi gas with artificial spin-orbit coupling can exhibit hysteresis loops of atomic currents. Cold atoms in ring-shape potentials are thus promising for demonstrating rate-dependent hysteresis and its associated phenomena.

  9. Effects of Off-Resonance Irradiation, Cross-Relaxation, and Chemical Exchange on Steady-State Magnetization and Effective Spin-Lattice Relaxation Times

    NASA Astrophysics Data System (ADS)

    Kingsley, Peter B.; Monahan, W. Gordon

    2000-04-01

    In the presence of an off-resonance radiofrequency field, recovery of longitudinal magnetization to a steady state is not purely monoexponential. Under reasonable conditions with zero initial magnetization, recovery is nearly exponential and an effective relaxation rate constant R1eff = 1/T1eff can be obtained. Exact and approximate formulas for R1eff and steady-state magnetization are derived from the Bloch equations for spins undergoing cross-relaxation and chemical exchange between two sites in the presence of an off-resonance radiofrequency field. The relaxation formulas require that the magnetization of one spin is constant, but not necessarily zero, while the other spin relaxes. Extension to three sites with one radiofrequency field is explained. The special cases of off-resonance effects alone and with cross-relaxation or chemical exchange, cross-relaxation alone, and chemical exchange alone are compared. The inaccuracy in saturation transfer measurements of exchange rate constants by published formulas is discussed for the creatine kinase reaction.

  10. The effect of a broad activation energy distribution on deuteron spin-lattice relaxation.

    PubMed

    Ylinen, E E; Punkkinen, M; Birczyński, A; Lalowicz, Z T

    2015-10-01

    Deuteron NMR spectra and spin-lattice relaxation were studied experimentally in zeolite NaY(2.4) samples containing 100% or 200% of CD3OH or CD3OD molecules of the total coverage of Na atoms in the temperature range 20-150K. The activation energies describing the methyl and hydroxyl motions show broad distributions. The relaxation data were interpreted by improving a recent model (Stoch et al., 2013 [16]) in which the nonexponential relaxation curves are at first described by a sum of three exponentials with adjustable relaxation rates and weights. Then a broad distribution of activation energies (the mean activation energy A0 and the width σ) was assumed for each essentially different methyl and hydroxyl position. The correlation times were calculated from the Arrhenius equation (containing the pre-exponential factor τ0), individual relaxation rates computed and classified into three classes, and finally initial relaxation rates and weights for each class formed. These were compared with experimental data, motional parameters changed slightly and new improved rates and weights for each class calculated, etc. This method was improved by deriving for the deuterons of the A and E species methyl groups relaxation rates, which depend explicitly on the tunnel frequency ωt. The temperature dependence of ωt and of the low-temperature correlation time were obtained by using the solutions of the Mathieu equation for a threefold potential. These dependencies were included in the simulations and as the result sets of A0, σ and τ0 obtained, which describe the methyl and hydroxyl motions in different positions in zeolite.

  11. Spin-lattice relaxation within a dimerized Ising chain in a magnetic field

    SciTech Connect

    Erdem, Rıza E-mail: rerdem29@hotmail.com; Gülpınar, Gül; Yalçın, Orhan; Pawlak, Andrzej

    2014-07-21

    A qualitative study of the spin-lattice relaxation within a dimerized Ising chain in a magnetic field is presented. We have first determined the time dependence of the deviation of the lattice distortion parameter δΔ from the equilibrium state within framework of a technique combining the statistical equilibrium theory based on the transfer matrix method and the linear theory of irreversible thermodynamics. We have shown that the time dependence of the lattice distortion parameter is characterized by a single time constant (τ) which diverges around the critical point in both dimerized (Δ≠0) and uniform (Δ=0) phase regions. When the temperature and magnetic field are fixed to certain values, the time τ depends only on exchange coupling between the spins. It is a characteristic time associated with the long wavelength fluctuations of distortion. We have also taken into account the effects of spatial fluctuations on the relaxation time using the full Landau-Ginzburg free energy functional. We have found an explicit expression for the relaxation time as a function of temperature, coupling constant and wave vector (q) and shown that the critical mode corresponds to the case q=0. Finally, our results are found to be in good qualitative agreement with the results obtained in recent experimental study on synchrotron x-ray scattering and muon spin relaxation in diluted material Cu{sub 1−y}Mg{sub y}GeO{sub 3} where the composition y is very close to 0.0209. These results can be considered as natural extensions of some previous works on static aspects of the problem.

  12. Spin-lattice relaxation of the methyl group protons in solids revisited: damped quantum rotation approach.

    PubMed

    Szymański, S

    2012-07-21

    Proton spin-lattice relaxation of the methyl group in solids had been one of the most thoroughly addressed theoretical problems in nuclear magnetic resonance (NMR) spectroscopy, considered at different levels of sophistication. For systems with substantial quantum tunneling effects, several quantum mechanical treatments were reported, although in practical applications the quantum models were always augmented with or replaced by the classical jump model. However, the latter has recently proved invalid in the description of NMR line shape effects in variable-temperature spectra of hindered methyl groups, while the competing theory of damped quantum rotation (DQR) was shown to be adequate. In this work, the spin-lattice relaxation issue for the methyl protons is readdressed using the latter theory. The main outcome is that, while the existing formulas for the relaxation rates remain unchanged, the crucial parameter entering them, the correlation time of the relevant random process, need to be reinterpreted. It proves to be the inverse of one of the two quantum-rate constants entering the DQR model, neither of which, when taken separately, can be related to the jump process. It can be identified with one describing the life-time broadening of the tunnel peaks in inelastic neutron scattering (INS) spectra of the methyl groups. Such a relationship between the relaxation and INS effects was reported from another laboratory long ago, but only for the low-temperature limit where thermal population of the excited torsional levels of the methyl group can be neglected. The whole spectrum of cases encountered in practical relaxation studies on protonated methyl groups is addressed for the first time. Preliminary experimental confirmation of this novel approach is reported, based on already published NMR data for a single crystal of methylmalonic acid. The once extensively debated issues of quenching of the coherent tunneling and of the classical limit in the dynamics of the

  13. Electron spin-lattice and spin-spin relaxation study of a trinuclear iron(III) complex and its relevance in quantum computing.

    PubMed

    Mitrikas, George; Sanakis, Yiannis; Raptopoulou, Catherine P; Kordas, George; Papavassiliou, Georgios

    2008-02-01

    Electron spins of molecular magnets are promising candidates for large scale quantum information processing because they exhibit a large number of low-lying excited states. In this paper X-band pulse electron paramagnetic resonance spectroscopy is used to determine the intrinsic relaxation times T1 and T2 of a molecular magnet with an S = 1/2 ground state, namely the neutral trinuclear oxo-centered iron (III) complex, [Fe3(micro3-O)(O2CPh)5(salox)(EtOH)(EtOH)(H2O)]. The temperature dependence of the spin-lattice relaxation time T1 between 4.5 and 11 K shows that the Orbach relaxation process is dominant with the first excited state lying 57 cm(-1) above the ground state, whereas the phase memory time T(M) is of the order of 2.6 micros and exhibits a modest temperature dependence. These results together with previous magnetic measurements give further insight into the magnetic properties of the complex. The coherent manipulation of the electron spins is also examined by means of transient nutation experiments.

  14. Electron spin relaxation in p-type GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Jiang, J. H.; Wu, M. W.

    2009-11-01

    We investigate electron spin relaxation in p-type GaAs quantum wells from a fully microscopic kinetic spin Bloch equation approach, with all the relevant scatterings, such as electron-impurity, electron-phonon, electron-electron Coulomb, electron-hole Coulomb and electron-hole exchange (the Bir-Aronov-Pikus (BAP) mechanism) scatterings, explicitly included. Via this approach, we examine the relative importance of the D'yakonov-Perel' (DP) and BAP mechanisms in wide ranges of temperature, hole density, excitation density and impurity density, and present a phase-diagram-like picture showing the parameter regime where the DP or BAP mechanism is more important. It is discovered that in the impurity-free case the temperature regime where the BAP mechanism is more efficient than the DP one is around the hole Fermi temperature for high hole density, regardless of excitation density. However, in the high impurity density case with the impurity density identical to the hole density, this regime is roughly from the electron Fermi temperature to the hole Fermi temperature. Moreover, we predict that for the impurity-free case, in the regime where the DP mechanism dominates the spin relaxation at all temperatures, the temperature dependence of the spin relaxation time (SRT) presents a peak around the hole Fermi temperature, which originates from the electron-hole Coulomb scattering. We also predict that at low temperature, the hole-density dependence of the electron SRT exhibits a double-peak structure in the impurity-free case, whereas it shows first a peak and then a valley in the case of identical impurity and hole densities. These intriguing behaviors are due to the contribution from holes in high subbands.

  15. Generalized Elliott-Yafet theory of electron spin relaxation in metals: origin of the anomalous electron spin lifetime in MgB2.

    PubMed

    Simon, F; Dóra, B; Murányi, F; Jánossy, A; Garaj, S; Forró, L; Bud'ko, S; Petrovic, C; Canfield, P C

    2008-10-24

    The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy difference between the conduction and a neighboring bands. The anomalous behavior is related to the unique band structure of MgB2 and the large electron-phonon coupling. The saturating spin relaxation is the spin transport analogue of the Ioffe-Regel criterion of electron transport.

  16. Insight into lithium transport in lithium nitridometallate battery materials from muon spin relaxation.

    PubMed

    Powell, Andrew S; Stoeva, Zlatka; Lord, James S; Smith, Ronald I; Gregory, Duncan H; Titman, Jeremy J

    2013-01-21

    Muon spin relaxation and powder neutron diffraction have been combined to study three lithium cobalt nitride battery materials. Neutron diffraction shows that these retain the P6/mmm space group of Li(3)N with Co located only on Li(1) sites. The lattice parameters vary smoothly with the degree of metal substitution, such that the [Li(2)N] layers expand while the layer separation contracts, as observed previously for similar series of Cu- and Ni-substituted materials. However, in contrast to the latter, the Li(3-x-y)Co(x)N phases exhibit Curie-Weiss paramagnetism and this prevents the use of nuclear magnetic resonance to measure Li(+) transport parameters. Therefore, muon spin relaxation has been employed here as an alternative technique to obtain quantitative information about Li(+) diffusion. Muon spin relaxation shows that Li(+) diffusion in Li(3-x-y)Co(x)N is anisotropic with transport confined to the [Li(2)N] plane at low temperature and exchange between Li(1) and Li(2) sites dominant at high temperature. By a comparison with previous studies some general trends have been established across a range of Cu-, Ni- and Co-substituted materials. For intra-layer diffusion E(a) decreases as metal substitution increases and the corresponding expansion of the layers results in a more open pathway for Li(+) diffusion. However, an optimal value of x is found with a ≈ 3.69 Å after which the concomitant contraction in layer spacing reduces the polarizability of the lattice framework.

  17. High Resolution 13C MRI With Hyperpolarized Urea: In Vivo T2 Mapping and 15N Labeling Effects

    PubMed Central

    Reed, Galen D.; von Morze, Cornelius; Bok, Robert; Koelsch, Bertram L.; Van Criekinge, Mark; Smith, Kenneth J.; Shang, Hong; Larson, Peder E. Z.; Kurhanewicz, John; Vigneron, Daniel B.

    2014-01-01

    13C steady state free precession (SSFP) magnetic resonance imaging and effective spin-spin relaxation time (T2) mapping were performed using hyperpolarized [13C] urea and [13C, 15N2] urea injected intravenously in rats. 15N labeling gave large T2 increases both in solution and in vivo due to the elimination of a strong scalar relaxation pathway. The T2 increase was pronounced in the kidney, with [13C, 15N2] urea giving T2 values of 6.3±1.3 s in the cortex and medulla, and 11±2 s in the renal pelvis. The measured T2 in the aorta was 1.3±0.3 s. [13C] urea showed shortened T2 values in the kidney of 0.23±0.03 s compared to 0.28±0.03 s measured in the aorta. The enhanced T2 of [13C, 15N2] urea was utilized to generate large signal enhancement by SSFP acquisitions with flip angles approaching the fully refocused regime. Projection images at 0.94 mm in-plane resolution were acquired with both urea isotopes, with [13C, 15N2] urea giving a greater than four-fold increase in signal-to-noise ratio [13C] over urea. PMID:24235273

  18. Local isotropic diffusion approximation for coupled internal and overall molecular motions in NMR spin relaxation.

    PubMed

    Gill, Michelle L; Palmer, Arthur G

    2014-09-25

    The present work demonstrates that NMR spin relaxation rate constants for molecules interconverting between states with different diffusion tensors can be modeled theoretically by combining orientational correlation functions for exchanging spherical molecules with locally isotropic approximations for the diffusion anisotropic tensors. The resulting expressions are validated by comparison with correlation functions obtained by Monte Carlo simulations and are accurate for moderate degrees of diffusion anisotropy typically encountered in investigations of globular proteins. The results are complementary to an elegant, but more complex, formalism that is accurate for all degrees of diffusion anisotropy [Ryabov, Y.; Clore, G. M.; Schwieters, C. D. J. Chem. Phys. 2012, 136, 034108].

  19. Flat-response spin-exchange relaxation free atomic magnetometer under negative feedback.

    PubMed

    Lee, Hyun Joon; Shim, Jeong Hyun; Moon, Han Seb; Kim, Kiwoong

    2014-08-25

    We demonstrate that the use of negative feedback extends the detection bandwidth of an atomic magnetometer in a spin-exchange relaxation free (SERF) regime. A flat-frequency response from zero to 190 Hz was achieved, which is nearly a three-fold enhancement while maintaining sensitivity, 3 fT/Hz1/2 at 100 Hz. With the extension of the bandwidth, the linear correlation between measured signals and a magne-tocardiographic field synthesized for comparison was increased from 0.21 to 0.74. This result supports the feasibility of measuring weak biomagnetic signals containing multiple frequency components using a SERF atomic magnetometer under negative feedback.

  20. Magnetocardiography with a modular spin-exchange relaxation free atomic magnetometer array

    PubMed Central

    Wyllie, R; Kauer, M; Smetana, G S; Wakai, R T; Walker, T G

    2012-01-01

    We present a portable four-channel atomic magnetometer array operating in the spin exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design and fibre coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6–11 fT Hz−1/2 single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room. PMID:22504066

  1. Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array.

    PubMed

    Wyllie, R; Kauer, M; Smetana, G S; Wakai, R T; Walker, T G

    2012-05-01

    We present a portable four-channel atomic magnetometer array operating in the spin-exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design and fibre-coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6-11 fT Hz(-1/2) single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room.

  2. A continued fraction resummation form of bath relaxation effect in the spin-boson model

    SciTech Connect

    Gong, Zhihao; Tang, Zhoufei; Wu, Jianlan; Mukamel, Shaul; Cao, Jianshu

    2015-02-28

    In the spin-boson model, a continued fraction form is proposed to systematically resum high-order quantum kinetic expansion (QKE) rate kernels, accounting for the bath relaxation effect beyond the second-order perturbation. In particular, the analytical expression of the sixth-order QKE rate kernel is derived for resummation. With higher-order correction terms systematically extracted from higher-order rate kernels, the resummed quantum kinetic expansion approach in the continued fraction form extends the Pade approximation and can fully recover the exact quantum dynamics as the expansion order increases.

  3. Auxiliary matrix formalism for interaction representation transformations, optimal control, and spin relaxation theories

    SciTech Connect

    Goodwin, D. L.; Kuprov, Ilya

    2015-08-28

    Auxiliary matrix exponential method is used to derive simple and numerically efficient general expressions for the following, historically rather cumbersome, and hard to compute, theoretical methods: (1) average Hamiltonian theory following interaction representation transformations; (2) Bloch-Redfield-Wangsness theory of nuclear and electron relaxation; (3) gradient ascent pulse engineering version of quantum optimal control theory. In the context of spin dynamics, the auxiliary matrix exponential method is more efficient than methods based on matrix factorizations and also exhibits more favourable complexity scaling with the dimension of the Hamiltonian matrix.

  4. Strain coupling mechanisms and elastic relaxation associated with spin state transitions in LaCoO3

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiying; Koppensteiner, Johannes; Schranz, Wilfried; Prabhakaran, Dharmalingam; Carpenter, Michael A.

    2011-04-01

    Advantage is taken of the wealth of experimental data relating to the evolution with temperature of spin states of Co3 + in LaCoO3 in order to undertake a detailed investigation of the mechanisms by which changes in electronic structure can influence strain, and elastic and anelastic relaxations in perovskites. The macroscopic strain accompanying changes in the spin state in LaCoO3 is predominantly a volume strain arising simply from the change in effective ionic radius of the Co3 + ions. This acts to renormalize the octahedral tilting transition temperature in a manner that is easily understood in terms of coupling between the tilt and spin order parameters. Results from resonant ultrasound spectroscopy at high frequencies (0.1-1.5 MHz) reveal stiffening of the shear modulus which scales qualitatively with a spin order parameter defined in terms of changing Co-O bond lengths. From this finding, in combination with results from dynamic mechanical analysis at low frequencies (0.1-50 Hz) and data from the literature, four distinctive anelastic relaxation mechanisms are identified. The relaxation times of these are displayed on an anelasticity map and are tentatively related to spin-spin relaxation, spin-lattice relaxation, migration of twin walls and migration of magnetic polarons. The effective activation energy for the freezing of twin wall motion below ~ 590 K at low frequencies was found to be 182 ± 21 kJ mol - 1 (1.9 ± 0.2 eV) which is attributed to pinning by pairs of oxygen vacancies, though the local mechanisms appear to have a spread of relaxation times. It seems inevitable that twin walls due to octahedral tilting must have quite different characteristics from the matrix in terms of local spin configurations of Co3 + . A hysteresis in the elastic properties at high temperatures further emphasizes the importance of oxygen content in controlling the properties of LaCoO3.

  5. Muon Spin Rotation/Relaxation Study of Ba2CoO4

    SciTech Connect

    Russo, P. L.; Sugiyama, J.; Brewer, J.; Ansaldo, E. J.; Stubbs, S. L.; Chow, K. H.; Jin, Rongying; Sha, Hao; Zhang, Jiandi

    2009-01-01

    A positive muon spin rotation and relaxation ({mu}{sup +}SR) experiment on a single crystal of Ba{sub 2}CoO{sub 4} indicates the existence of an antiferromagnetic (AF) transition occurring at T{sub N} {approx} 24 K. Weak transverse field measurements show that the paramagnetic volume fraction of the sample decreases rapidly at the magnetic transition, indicating a bulk effect which cannot be due to the presence of impurities. Zero-field measurements reveal the presence of a magnetically ordered state below T{sub N} with at least three crystallographically inequivalent muon sites. The results are compared to recent magnetic susceptibility and neutron measurements. Of the two AF spin structures proposed to explain recent neutron experiments, the {mu}{sup +}SR results clearly exclude the one involving AF order along the c axis while supporting that with AF order in the ab plane.

  6. Hyperfine-induced spin relaxation of a hopping carrier: implications for spin transport in 1-D vs 3-D organic semiconductors

    NASA Astrophysics Data System (ADS)

    Mkhitaryan, Vagharsh; Dobrovitski, Viatcheslav; 0 Team

    2015-03-01

    The hyperfine coupling of a carrier spin to a nuclear spin bath is a predominant channel for the carrier spin relaxation in organic semiconductors. We investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice theoretically, in a transport regime typical for organic semiconductors. We show that in d = 1 and d = 2 the time dependence of spin polarization, P (t) , is dominated by a superexponential decay, crossing over to an exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P (t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d = 1 vs. d = 3). Furthermore, we consider the coordinate dependence of spin polarization, σ (r) , in a hypothetic lateral or vertical organic spin-valve device. We demonstrate that, while σ (r) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the specific field-dependence of spin relaxation length. This work was supported by the Department of Energy-Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

  7. Membrane fluidity profiles as deduced by saturation-recovery EPR measurements of spin-lattice relaxation times of spin labels

    PubMed Central

    Mainali, Laxman; Feix, Jimmy B.; Hyde, James S.; Subczynski, Witold K.

    2011-01-01

    There are no easily obtainable EPR spectral parameters for lipid spin labels that describe profiles of membrane fluidity. The order parameter, which is most often used as a measure of membrane fluidity, describes the amplitude of wobbling motion of alkyl chains relative to the membrane normal and does not contain explicitly time or velocity. Thus, this parameter can be considered as nondynamic. The spin-lattice relaxation rate (T−11) obtained from saturation-recovery EPR measurements of lipid spin labels in deoxygenated samples depends primarily on the rotational correlation time of the nitroxide moiety within the lipid bilayer. Thus, T−11 can be used as a convenient quantitative measure of membrane fluidity that reflects local membrane dynamics. T−11 profiles obtained for 1-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine (n-PC) spin labels in dimyristoylphosphatidylcholine (DMPC) membranes with and without 50 mol% cholesterol are presented in parallel with profiles of the rotational diffusion coefficient, R⊥, obtained from simulation of EPR spectra using Freed's model. These profiles are compared with profiles of the order parameter obtained directly from EPR spectra and with profiles of the order parameter obtained from simulation of EPR spectra. It is shown that T−11 and R⊥ profiles reveal changes in membrane fluidity that depend on the motional properties of the lipid alkyl chain. We find that cholesterol has a rigidifying effect only to the depth occupied by the rigid steroid ring structure and a fluidizing effect at deeper locations. These effects cannot be differentiated by profiles of the order parameter. All profiles in this study were obtained at X-band (9.5 GHz). PMID:21868272

  8. Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions

    NASA Astrophysics Data System (ADS)

    Lewis, Alan M.; Manolopoulos, David E.; Hore, P. J.

    2014-07-01

    We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nuclear spins which has recently been used to establish a "proof of principle" for the operation of a chemical compass [K. Maeda, K. B. Henbest, F. Cintolesi, I. Kuprov, C. T. Rodgers, P. A. Liddell, D. Gust, C. R. Timmel, and P. J. Hore, Nature (London) 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C.+PF.- radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical.

  9. Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions.

    PubMed

    Lewis, Alan M; Manolopoulos, David E; Hore, P J

    2014-07-28

    We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nuclear spins which has recently been used to establish a "proof of principle" for the operation of a chemical compass [K. Maeda, K. B. Henbest, F. Cintolesi, I. Kuprov, C. T. Rodgers, P. A. Liddell, D. Gust, C. R. Timmel, and P. J. Hore, Nature (London) 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C(·+)PF(·-) radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical. PMID:25084885

  10. Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions

    SciTech Connect

    Lewis, Alan M.; Manolopoulos, David E.; Hore, P. J.

    2014-07-28

    We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nuclear spins which has recently been used to establish a “proof of principle” for the operation of a chemical compass [K. Maeda, K. B. Henbest, F. Cintolesi, I. Kuprov, C. T. Rodgers, P. A. Liddell, D. Gust, C. R. Timmel, and P. J. Hore, Nature (London) 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C{sup ·+}PF{sup ·−} radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical.

  11. Competition between photoexcitation and relaxation in spin-crossover complexes in the frame of a mechanoelastic model

    NASA Astrophysics Data System (ADS)

    Enachescu, Cristian; Stoleriu, Laurentiu; Stancu, Alexandru; Hauser, Andreas

    2010-09-01

    In this paper we use a recently proposed elastic model in order to study the competition between linear photoexcitation and cooperative relaxation in spin-crossover molecular magnets. The difference in molecular size between the two possible spin states, that is, the high-spin and the low-spin states, respectively, induces distortions of the crystal lattice. These determine the elastic interactions between molecules, treated here as connecting springs that are either compressed or extended from their equilibrium length, thus modulating the local probability for the high-spin→low-spin relaxation. The crossover of individual molecules within the lattice is checked by a standard Monte Carlo procedure. Using very simple assumptions and a minimum number of parameters, photoexcitation curves and hysteresis loops under continuous irradiation below the thermal transition temperature can thus be simulated. The formation of clusters is analyzed and the presence of inhomogeneities in the system is investigated.

  12. Longitudinal relaxation in dipole-coupled homonuclear three-spin systems: Distinct correlations and odd spectral densities

    SciTech Connect

    Chang, Zhiwei; Halle, Bertil

    2015-12-21

    A system of three dipole-coupled spins exhibits a surprisingly intricate relaxation behavior. Following Hubbard’s pioneering 1958 study, many authors have investigated different aspects of this problem. Nevertheless, on revisiting this classic relaxation problem, we obtain several new results, some of which are at variance with conventional wisdom. Most notably from a fundamental point of view, we find that the odd-valued spectral density function influences longitudinal relaxation. We also show that the effective longitudinal relaxation rate for a non-isochronous three-spin system can exhibit an unusual inverted dispersion step. To clarify these and other issues, we present a comprehensive theoretical treatment of longitudinal relaxation in a three-spin system of arbitrary geometry and with arbitrary rotational dynamics. By using the Liouville-space formulation of Bloch-Wangsness-Redfield theory and a basis of irreducible spherical tensor operators, we show that the number of relaxation components in the different cases can be deduced from symmetry arguments. For the isochronous case, we present the relaxation matrix in analytical form, whereas, for the non-isochronous case, we employ a computationally efficient approach based on the stochastic Liouville equation.

  13. Longitudinal relaxation in dipole-coupled homonuclear three-spin systems: Distinct correlations and odd spectral densities

    NASA Astrophysics Data System (ADS)

    Chang, Zhiwei; Halle, Bertil

    2015-12-01

    A system of three dipole-coupled spins exhibits a surprisingly intricate relaxation behavior. Following Hubbard's pioneering 1958 study, many authors have investigated different aspects of this problem. Nevertheless, on revisiting this classic relaxation problem, we obtain several new results, some of which are at variance with conventional wisdom. Most notably from a fundamental point of view, we find that the odd-valued spectral density function influences longitudinal relaxation. We also show that the effective longitudinal relaxation rate for a non-isochronous three-spin system can exhibit an unusual inverted dispersion step. To clarify these and other issues, we present a comprehensive theoretical treatment of longitudinal relaxation in a three-spin system of arbitrary geometry and with arbitrary rotational dynamics. By using the Liouville-space formulation of Bloch-Wangsness-Redfield theory and a basis of irreducible spherical tensor operators, we show that the number of relaxation components in the different cases can be deduced from symmetry arguments. For the isochronous case, we present the relaxation matrix in analytical form, whereas, for the non-isochronous case, we employ a computationally efficient approach based on the stochastic Liouville equation.

  14. Higher triplet state of fullerene C{sub 70} revealed by electron spin relaxation

    SciTech Connect

    Uvarov, Mikhail N.; Behrends, Jan; Kulik, Leonid V.

    2015-12-28

    Spin-lattice relaxation times T{sub 1} of photoexcited triplets {sup 3}C{sub 70} in glassy decalin were obtained from electron spin echo inversion recovery dependences. In the range 30–100 K, the temperature dependence of T{sub 1} was fitted by the Arrhenius law with an activation energy of 172 cm{sup −1}. This indicates that the dominant relaxation process of {sup 3}C{sub 70} is described by an Orbach-Aminov mechanism involving the higher triplet state t{sub 2} which lies 172 cm{sup −1} above the lowest triplet state t{sub 1}. Chemical modification of C{sub 70} fullerene not only decreases the intrinsic triplet lifetime by about ten times but also increases T{sub 1} by several orders of magnitude. The reason for this is the presence of a low-lying excited triplet state in {sup 3}C{sub 70} and its absence in triplet C{sub 70} derivatives. The presence of the higher triplet state in C{sub 70} is in good agreement with the previous results from phosphorescence spectroscopy.

  15. Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation.

    PubMed

    Bhattacharyya, Amitava; Adroja, Devashibhai; Kase, Naoki; Hillier, Adrian; Akimitsu, Jun; Strydom, Andre

    2015-01-01

    Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high-temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 ( TC= 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T(3) dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s-wave superconductor. The temperature dependence of the deduced superfluid in density Y5Rh6Sn18 is consistent with a BCS s-wave gap function, while the zero-field muon spin relaxation measurements strongly evidences unconventional superconductivity through a spontaneous appearance of an internal magnetic field below the superconducting transition temperature, signifying that the superconducting state is categorized by the broken time-reversal symmetry. PMID:26286229

  16. Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation

    PubMed Central

    Bhattacharyya, Amitava; Adroja, Devashibhai; Kase, Naoki; Hillier, Adrian; Akimitsu, Jun; Strydom, Andre

    2015-01-01

    Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high—temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 ( TC= 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T3 dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s—wave superconductor. The temperature dependence of the deduced superfluid in density Y5Rh6Sn18 is consistent with a BCS s—wave gap function, while the zero-field muon spin relaxation measurements strongly evidences unconventional superconductivity through a spontaneous appearance of an internal magnetic field below the superconducting transition temperature, signifying that the superconducting state is categorized by the broken time-reversal symmetry. PMID:26286229

  17. Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation.

    PubMed

    Bhattacharyya, Amitava; Adroja, Devashibhai; Kase, Naoki; Hillier, Adrian; Akimitsu, Jun; Strydom, Andre

    2015-08-19

    Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high-temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 ( TC= 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T(3) dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s-wave superconductor. The temperature dependence of the deduced superfluid in density Y5Rh6Sn18 is consistent with a BCS s-wave gap function, while the zero-field muon spin relaxation measurements strongly evidences unconventional superconductivity through a spontaneous appearance of an internal magnetic field below the superconducting transition temperature, signifying that the superconducting state is categorized by the broken time-reversal symmetry.

  18. Far-from-Equilibrium Field Theory of Many-Body Quantum Spin Systems: Prethermalization and Relaxation of Spin Spiral States in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Babadi, Mehrtash; Demler, Eugene; Knap, Michael

    2015-10-01

    We study theoretically the far-from-equilibrium relaxation dynamics of spin spiral states in the three-dimensional isotropic Heisenberg model. The investigated problem serves as an archetype for understanding quantum dynamics of isolated many-body systems in the vicinity of a spontaneously broken continuous symmetry. We present a field-theoretical formalism that systematically improves on the mean field for describing the real-time quantum dynamics of generic spin-1 /2 systems. This is achieved by mapping spins to Majorana fermions followed by a 1 /N expansion of the resulting two-particle-irreducible effective action. Our analysis reveals rich fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral states. In particular, we find the sudden appearance of long-lived prethermalized plateaus with diverging lifetimes as the spiral winding is tuned toward the thermodynamically stable ferro- or antiferromagnetic phases. The emerging prethermalized states are characterized by different bosonic modes being thermally populated at different effective temperatures and by a hierarchical relaxation process reminiscent of glassy systems. Spin-spin correlators found by solving the nonequilibrium Bethe-Salpeter equation provide further insight into the dynamic formation of correlations, the fate of unstable collective modes, and the emergence of fluctuation-dissipation relations. Our predictions can be verified experimentally using recent realizations of spin spiral states with ultracold atoms in a quantum gas microscope [S. Hild et al., Phys. Rev. Lett. 113, 147205 (2014), 10.1103/PhysRevLett.113.147205].

  19. Coexisting static magnetic ordering and superconductivity in CeCu2.1Si2 found by muon spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Schone, H. E.; Kempton, J. R.; Stronach, C. E.; Barth, S.; Gygax, F. N.; Hitti, B.; Schenck, A.

    1988-01-01

    Zero- and longitudinal-field muon spin relaxation measurements on a heavy fermion system CeCu2.1 Si2 have revealed an onset of static magnetic ordering below T(M) approximately 0.8 K, which coexists with superconductivity below T(c) = 0.7 K. The line shapes of the observed muon spin depolarization functions suggest an ordering in either spin glass or incommensurate spin-density-wave state, with a small averaged static moment of the order of 0.1 micro-B per formula unit at T approaches 0.

  20. Electron spin relaxation time measurements using radiofrequency longitudinally detected ESR and application in oximetry.

    PubMed

    Panagiotelis, I; Nicholson, I; Hutchison, J M

    2001-03-01

    Longitudinally detected ESR (LODESR) involves transverse ESR irradiation with a modulated source and observing oscillations in the spin magnetization parallel to the main magnetic field. In this study, radiofrequency-LODESR was used for oximetry by measuring the relaxation times of the electron. T1e and T2e were measured by investigating LODESR signal magnitude as a function of detection frequency. We have also predicted theoretically and verified experimentally the LODESR signal phase dependence on detection frequency and relaxation times. These methods are valid even for inhomogeneous lines provided that T1e>T2e. We have also developed a new method for measuring T1e, valid for inhomogeneous spectra, for all values of T1e and T2e, based on measuring the spectral area as a function of detection frequency. We have measured T1e and T2e for lithium phthalocyanine crystals, for the nitroxide TEMPOL, and for the single line agent Triarylmethyl (TAM). Furthermore, we have collected spectra from aqueous solutions of TEMPOL and TAM at different oxygen concentrations and confirmed that T1e values are reduced with increased oxygen concentration. We have also measured the spin-lattice electronic relaxation time for degassed aqueous solutions of the same agents at different agent concentrations. T1e decreases as a function of concentration for TAM while it remains independent of free radical concentration for TEMPOL, a major advantage for oxygen mapping. This method, combined with the ability of LODESR to provide images of exogenous free radicals in vivo, presents an attractive alternative to the conventional transverse ESR linewidth based oximetry methods.

  1. Temperature dependence of the NMR relaxation rate 1 /T1 for quantum spin chains

    NASA Astrophysics Data System (ADS)

    Dupont, Maxime; Capponi, Sylvain; Laflorencie, Nicolas

    2016-10-01

    We present results of numerical simulations performed on one-dimensional spin chains in order to extract the so-called relaxation rate 1 /T1 accessible through NMR experiments. Building on numerical tensor network methods using the matrix product states formalism, we can follow the nontrivial crossover occurring in critical chains between the high-temperature diffusive classical regime and the low-temperature response described by the Tomonaga-Luttinger liquid (TLL) theory, for which analytical expressions are known. In order to compare analytics and numerics, we focus on a generic spin-1 /2 X X Z chain which is a paradigm of gapless TLL, as well as a more realistic spin-1 anisotropic chain, modeling the DTN material, which can be either in a trivial gapped phase or in a TLL regime induced by an external magnetic field. Thus, by monitoring the finite temperature crossover, we provide quantitative limits on the range of validity of TLL theory, that will be useful when interpreting experiments on quasi-one-dimensional materials.

  2. Spin relaxation and intervalley scattering in 2D semiconductors (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Hanbicki, Aubrey; Currie, Marc; Kioseoglou, George; Hellberg, C. Stephen; McCreary, Kathleen M.; Friedman, Adam L.; Jonker, Berend T.

    2015-09-01

    Monolayer transition metal dichalcogenides, MX2 (M = Mo, W and X = S, Se), are direct-gap semiconductors with some interesting properties. First, the low-dimensional hexagonal structure leads to two inequivalent K-points, K and K', in the brillioun zone. Second, this valley index and spin are intrinsically coupled, and spin-dependent selection rules enable one to independently populate and interrogate a unique K valley with circularly polarized light. Here we probe the degree of circular polarization of the emitted photoluminescence as function of the photo-excitation energy and temperature to elucidate spin-dependent inter- and intra-valley relaxation mechanisms. Monolayer flakes of MoS2 and MoSe2 show a strong depolarization as the excitation energy is increased. However, WS2 maintains significant polarization for high excitation energies, even at room temperature when properly prepared. We discuss the behavior of the polarization in terms of various phonon assisted intervalley scattering processes. This work was supported by NRL and the NRL Nanoscience Institute

  3. Room-temperature electron spin relaxation of nitroxides immobilized in trehalose: Effect of substituents adjacent to NO-group

    NASA Astrophysics Data System (ADS)

    Kuzhelev, Andrey A.; Strizhakov, Rodion K.; Krumkacheva, Olesya A.; Polienko, Yuliya F.; Morozov, Denis A.; Shevelev, Georgiy Yu.; Pyshnyi, Dmitrii V.; Kirilyuk, Igor A.; Fedin, Matvey V.; Bagryanskaya, Elena G.

    2016-05-01

    Trehalose has been recently promoted as efficient immobilizer of biomolecules for room-temperature EPR studies, including distance measurements between attached nitroxide spin labels. Generally, the structure of nitroxide influences the electron spin relaxation times, being crucial parameters for room-temperature pulse EPR measurements. Therefore, in this work we investigated a series of nitroxides with different substituents adjacent to NO-moiety including spirocyclohexane, spirocyclopentane, tetraethyl and tetramethyl groups. Electron spin relaxation times (T1, Tm) of these radicals immobilized in trehalose were measured at room temperature at X- and Q-bands (9/34 GHz). In addition, a comparison was made with the corresponding relaxation times in nitroxide-labeled DNA immobilized in trehalose. In all cases phase memory times Tm were close to 700 ns and did not essentially depend on structure of substituents. Comparison of temperature dependences of Tm at T = 80-300 K shows that the benefit of spirocyclohexane substituents well-known at medium temperatures (∼100-180 K) becomes negligible at 300 K. Therefore, unless there are specific interactions between spin labels and biomolecules, the room-temperature value of Tm in trehalose is weakly dependent on the structure of substituents adjacent to NO-moiety of nitroxide. The issues of specific interactions and stability of nitroxide labels in biological media might be more important for room temperature pulsed dipolar EPR than differences in intrinsic spin relaxation of radicals.

  4. Optical Transient-Grating Measurements of Spin Diffusion andRelaxation in a Two-Dimensional Electron Gas

    SciTech Connect

    Weber, Christopher Phillip

    2005-01-01

    Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field.

  5. Muon spin relaxation study of the magnetism in unilluminated Prussian Blue analogue photomagnets

    NASA Astrophysics Data System (ADS)

    Salman, Z.; Parolin, T. J.; Chow, K. H.; Keeler, T. A.; Miller, R. I.; Wang, D.; Macfarlane, W. A.

    2006-05-01

    We present longitudinal field muon spin relaxation (μSR) measurements in the unilluminated state of the photosensitive molecular magnetic Co-Fe Prussian Blue analogues M1-2xCo1+x[Fe(CN)6]•zH2O , where M=K and Rb with x=0.4 and ≃0.17 , respectively. These results are compared to those obtained in the x=0.5 stoichiometric limit Co1.5[Fe(CN)6]•6H2O , which is not photosensitive. We find evidence for correlation between the range of magnetic ordering and the value of x in the unilluminated state, which can be explained using a site percolation model.

  6. Study of the operation temperature in the spin-exchange relaxation free magnetometer

    SciTech Connect

    Fang, Jiancheng; Li, Rujie Duan, Lihong; Chen, Yao; Quan, Wei

    2015-07-15

    We study the influence of the cell temperature on the sensitivity of the spin-exchange relaxation free (SERF) magnetometer and analyze the possibility of operating at a low temperature. Utilizing a 25 × 25 × 25 mm{sup 3} Cs vapor cell with a heating temperature of 85 {sup ∘}C, which is almost half of the value of potassium, we obtain a linewidth of 1.37 Hz and achieve a magnetic field sensitivity of 55 fT/Hz{sup 1/2} in a single channel. Theoretical analysis shows that fundamental sensitivity limits of this device with an active volume of 1 cm{sup 3} could approach 1 fT/Hz{sup 1/2}. Taking advantage of the higher saturated vapor pressure, SERF magnetometer based on Cs opens up the possibility for low cost and portable sensors and is particularly appropriate for lower temperature applications.

  7. Study of the operation temperature in the spin-exchange relaxation free magnetometer.

    PubMed

    Fang, Jiancheng; Li, Rujie; Duan, Lihong; Chen, Yao; Quan, Wei

    2015-07-01

    We study the influence of the cell temperature on the sensitivity of the spin-exchange relaxation free (SERF) magnetometer and analyze the possibility of operating at a low temperature. Utilizing a 25 × 25 × 25 mm(3) Cs vapor cell with a heating temperature of 85 °C, which is almost half of the value of potassium, we obtain a linewidth of 1.37 Hz and achieve a magnetic field sensitivity of 55 fT/Hz(1/2) in a single channel. Theoretical analysis shows that fundamental sensitivity limits of this device with an active volume of 1 cm(3) could approach 1 fT/Hz(1/2). Taking advantage of the higher saturated vapor pressure, SERF magnetometer based on Cs opens up the possibility for low cost and portable sensors and is particularly appropriate for lower temperature applications.

  8. Magnetic trapping of silver and copper, and anomalous spin relaxation in the ag-he system.

    PubMed

    Brahms, Nathan; Newman, Bonna; Johnson, Cort; Greytak, Tom; Kleppner, Daniel; Doyle, John

    2008-09-01

    We have trapped large numbers of copper (Cu) and silver (Ag) atoms using buffer-gas cooling. Up to 3 x 10{12} Cu atoms and 4 x 10{13} Ag atoms are trapped. Lifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios of elastic to inelastic collision rates with He are >or=10{6}, suggesting Cu and Ag are favorable for use in ultracold applications. The temperature dependence of the Ag-3He collision rate varies as T;{5.8+/-0.4}. We find that this temperature dependence is inconsistent with the behavior predicted for relaxation arising from the spin-rotation interaction, and conclude that the Ag-3He system displays anomalous collisional behavior in the multiple-partial wave regime. Gold (Au) was ablated into 3He buffer gas, however, atomic Au lifetimes were observed to be too short to permit trapping.

  9. Nitrogen nuclear spin flips in nitroxide spin probes of different sizes in glassy o-terphenyl: Possible relation with α- and β-relaxations

    NASA Astrophysics Data System (ADS)

    Isaev, N. P.; Dzuba, S. A.

    2011-09-01

    The pulsed electron-electron double resonance (ELDOR) technique was employed to study nitroxide spin probes of three different sizes dissolved in glassy o-terphenyl. A microwave pulse applied to the central hyperfine structure (hfs) component of the nitroxide electron paramagnetic resonance spectrum was followed by two echo-detecting pulses of different microwave frequency to probe the magnetization transfer (MT) to the low-field hfs component. The MT between hfs components is readily related to flips in the nitrogen nuclear spin, which in turn are induced by molecular motion. The MT on the time scale of tens of microseconds was observed over a wide temperature range, including temperatures near and well below the glass transition. For a bulky nitroxide, it was found that MT rates approach dielectric α (primary) relaxation frequencies reported for o-terphenyl in the literature. For small nitroxides, MT rates were found to match the frequencies of dielectric β (secondary) Johari-Goldstein relaxation. The most probable motional mechanism inducing the nitrogen nuclear spin flips is large-angle angular jumps, between some orientations of unequal occupation probabilities. The pulsed ELDOR of nitroxide spin probes may provide additional insight into the nature of Johari-Goldstein relaxation in glassy media and may serve as a tool for studying this relaxation in substances consisting of non-rigid molecules (such as branched polymers) and in heterogeneous and non-polar systems (such as a core of biological membranes).

  10. Transverse spin relaxation and diffusion-constant measurements of spin-polarized 129Xe nuclei in the presence of a magnetic field gradient

    PubMed Central

    Liu, Xiaohu; Chen, Chang; Qu, Tianliang; Yang, Kaiyong; Luo, Hui

    2016-01-01

    The presence of a magnetic field gradient in a sample cell containing spin-polarized 129Xe atoms will cause an increased relaxation rate. We measured the transverse spin relaxation time of 129Xe verse the applied magnetic field gradient and the cell temperature. We then compared the different transverse spin relaxation behavior of dual isotopes of xenon (129Xe and 131Xe) due to magnetic field gradient in the same cell. The experiment results show the residual magnetic field gradient can be measured and compensated by applying a negative magnetic gradient in the sample cell. The transverse spin relaxation time of 129Xe could be increased 2–7 times longer when applying an appropriate magnetic field gradient. The experiment results can also be used to determine the diffusion constant of 129Xe in H2 and N2 to be 0.4 ± 0.26 cm2/sec and 0.12 ± 0.02 cm2/sec. The results are close with theoretical calculation. PMID:27049237

  11. Transverse spin relaxation and diffusion-constant measurements of spin-polarized 129Xe nuclei in the presence of a magnetic field gradient.

    PubMed

    Liu, Xiaohu; Chen, Chang; Qu, Tianliang; Yang, Kaiyong; Luo, Hui

    2016-01-01

    The presence of a magnetic field gradient in a sample cell containing spin-polarized (129)Xe atoms will cause an increased relaxation rate. We measured the transverse spin relaxation time of (129)Xe verse the applied magnetic field gradient and the cell temperature. We then compared the different transverse spin relaxation behavior of dual isotopes of xenon ((129)Xe and (131)Xe) due to magnetic field gradient in the same cell. The experiment results show the residual magnetic field gradient can be measured and compensated by applying a negative magnetic gradient in the sample cell. The transverse spin relaxation time of (129)Xe could be increased 2-7 times longer when applying an appropriate magnetic field gradient. The experiment results can also be used to determine the diffusion constant of (129)Xe in H2 and N2 to be 0.4 ± 0.26 cm(2)/sec and 0.12 ± 0.02 cm(2)/sec. The results are close with theoretical calculation. PMID:27049237

  12. Room-Temperature Electron Spin Relaxation of Triarylmethyl Radicals at X- and Q-bands

    PubMed Central

    Krumkacheva, Olesya A.; Strizhakov, Rodion K.; Rogozhnikova, Olga Yu.; Troitskaya, Tatiana I.

    2016-01-01

    Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form) , mono-, di-, and tri-ester derivatives of Finland-D36 trityl, deuterated form of OX63, dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed Electron Paramagnetic Resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm~T2) on magnetic field: room-temperature Tm values are ~1.5-2.5 times smaller at Q-band (34 GHz, 1.2 T) compared to X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligible at lower magnetic fields but comes into play at Q-band. In agreement with this, while T1~Tm at X-band, we observe T1>Tm at Q-band due to increased contributions from incomplete motional averaging of g-anisotropy. In addition, the viscosity dependence shows that (1/Tm-1/T1) is proportional to the tumbling correlation time of trityls. Based on the analysis of previous data and results of the present work, we conclude that in general situation where spin label is at least partly mobile, X-band is most suitable for application of trityls for room-temperature pulsed EPR distance measurements. PMID:26001103

  13. Distribution of Pico- and Nanosecond Motions in Disordered Proteins from Nuclear Spin Relaxation.

    PubMed

    Khan, Shahid N; Charlier, Cyril; Augustyniak, Rafal; Salvi, Nicola; Déjean, Victoire; Bodenhausen, Geoffrey; Lequin, Olivier; Pelupessy, Philippe; Ferrage, Fabien

    2015-09-01

    Intrinsically disordered proteins and intrinsically disordered regions (IDRs) are ubiquitous in the eukaryotic proteome. The description and understanding of their conformational properties require the development of new experimental, computational, and theoretical approaches. Here, we use nuclear spin relaxation to investigate the distribution of timescales of motions in an IDR from picoseconds to nanoseconds. Nitrogen-15 relaxation rates have been measured at five magnetic fields, ranging from 9.4 to 23.5 T (400-1000 MHz for protons). This exceptional wealth of data allowed us to map the spectral density function for the motions of backbone NH pairs in the partially disordered transcription factor Engrailed at 11 different frequencies. We introduce an approach called interpretation of motions by a projection onto an array of correlation times (IMPACT), which focuses on an array of six correlation times with intervals that are equidistant on a logarithmic scale between 21 ps and 21 ns. The distribution of motions in Engrailed varies smoothly along the protein sequence and is multimodal for most residues, with a prevalence of motions around 1 ns in the IDR. We show that IMPACT often provides better quantitative agreement with experimental data than conventional model-free or extended model-free analyses with two or three correlation times. We introduce a graphical representation that offers a convenient platform for a qualitative discussion of dynamics. Even when relaxation data are only acquired at three magnetic fields that are readily accessible, the IMPACT analysis gives a satisfactory characterization of spectral density functions, thus opening the way to a broad use of this approach. PMID:26331256

  14. Distribution of Pico- and Nanosecond Motions in Disordered Proteins from Nuclear Spin Relaxation

    PubMed Central

    Khan, Shahid N.; Charlier, Cyril; Augustyniak, Rafal; Salvi, Nicola; Déjean, Victoire; Bodenhausen, Geoffrey; Lequin, Olivier; Pelupessy, Philippe; Ferrage, Fabien

    2015-01-01

    Intrinsically disordered proteins and intrinsically disordered regions (IDRs) are ubiquitous in the eukaryotic proteome. The description and understanding of their conformational properties require the development of new experimental, computational, and theoretical approaches. Here, we use nuclear spin relaxation to investigate the distribution of timescales of motions in an IDR from picoseconds to nanoseconds. Nitrogen-15 relaxation rates have been measured at five magnetic fields, ranging from 9.4 to 23.5 T (400–1000 MHz for protons). This exceptional wealth of data allowed us to map the spectral density function for the motions of backbone NH pairs in the partially disordered transcription factor Engrailed at 11 different frequencies. We introduce an approach called interpretation of motions by a projection onto an array of correlation times (IMPACT), which focuses on an array of six correlation times with intervals that are equidistant on a logarithmic scale between 21 ps and 21 ns. The distribution of motions in Engrailed varies smoothly along the protein sequence and is multimodal for most residues, with a prevalence of motions around 1 ns in the IDR. We show that IMPACT often provides better quantitative agreement with experimental data than conventional model-free or extended model-free analyses with two or three correlation times. We introduce a graphical representation that offers a convenient platform for a qualitative discussion of dynamics. Even when relaxation data are only acquired at three magnetic fields that are readily accessible, the IMPACT analysis gives a satisfactory characterization of spectral density functions, thus opening the way to a broad use of this approach. PMID:26331256

  15. Importance of cross-correlated relaxation in the spectra of simple organofluorine compounds: Spectral complexity of A3B3X spin systems compared to ABX spin systems

    NASA Astrophysics Data System (ADS)

    Alemany, Lawrence B.; Malloy, Thomas B.; Nunes, Megan M.; Zaibaq, Nicholas G.

    2012-09-01

    In a continuation of our initial investigation of the complex 13C and 19F spectra exhibited by two simple organofluorine compounds, additional organofluorine compounds expected to exhibit a wide range of spectral complexity were studied. Spectral simulations are critical for analyzing the more complex spin systems, in particular, A3B3X and A6B3X. Cross-correlated relaxation is commonly observed; examples of 13Csbnd 19F cross-correlated relaxation are shown with the signals for each nucleus exhibiting unequal relaxation rates. Higher order effects are particularly noticeable in the spectra of perfluoro-t-butyl alcohol because of a large 4JFF value in the (13CF3)(12CF3)212COH isotopomer. The many additional transitions in an A3B3X spin system compared to an ABX spin system result in much more complex 19F (A3 and B3) and 13C (X) spectra, even though only three types of nuclei are involved in each spin system. The corresponding protio compounds typically constitute a much simpler A3M3X spin system because the long-range nJHH coupling (n ⩾ 4) is much smaller than the corresponding long-range nJFF coupling. Spectra previously published for ethane-1-13C (A3B3X) and hexafluoroethane-1-13C (A3M3X) are notable exceptions and are discussed.

  16. Magnetic Field-Independent Onset of Vortex Pinning up to 28 T by ^17O Spin-spin Relaxation in YBa_2Cu_3O_7

    NASA Astrophysics Data System (ADS)

    Bachman, H. N.; Mitrovic, V. F.; Reyes, A. P.; Halperin, W. P.; Kleinhammes, A.; Kuhns, P.; Moulton, W. G.

    1998-03-01

    We report spin-spin relaxation measurements (T_2) up to 28 T. The data confirm a field-independent pinning temperature from ≈10 T up to 28 T for aligned YBa_2Cu_3O7 powder. Below ≈10 T the pinning temperature is field-dependent, and is consistent with the melting temperature of clean, untwinned YBCO crystals (Reyes, et al.), Phys. Rev. B, 55, R14737, (1997).. Spectrum analysis shows that above ≈10 T the pinning temperature is field-independent, occurring at 80 K (H. N. Bachman, et al.), Bull. Am. Phys. Soc., 42, 661, (1997).. Spin-spin relaxation probes the z-axis fluctuations in magnetic field which arise from copper and oxygen spin fluctuations (T1 processes) and field fluctuations from vortices. The vortex contribution is observable only for vortices locally fluctuating in the pinned or frozen state. The vortex field fluctuations have a lorentzian spectral density, in contrast to the normal state relaxation which is well described by a gaussian. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity. The NHMFL is supported through the NSF and the state of Florida.

  17. The Long-term Post-outburst Spin Down and Flux Relaxation of Magnetar Swift J1822.3-1606

    NASA Astrophysics Data System (ADS)

    Scholz, P.; Kaspi, V. M.; Cumming, A.

    2014-05-01

    The magnetar Swift J1822.3-1606 entered an outburst phase in 2011 July. Previous X-ray studies of its post-outburst rotational evolution yielded inconsistent measurements of the spin-inferred magnetic field. Here we present the timing behavior and flux relaxation from over two years of Swift, RXTE, and Chandra observations following the outburst. We find that the ambiguity in previous timing solutions was due to enhanced spin down that resembles an exponential recovery following a glitch at the outburst onset. After fitting out the effects of the recovery, we measure a long-term spin-down rate of \\dot{\

  18. Solution NMR Structure Determination of Polytopic α-Helical Membrane Proteins: A Guide to Spin Label Paramagnetic Relaxation Enhancement Restraints.

    PubMed

    Columbus, Linda; Kroncke, Brett

    2015-01-01

    Solution nuclear magnetic resonance structures of polytopic α-helical membrane proteins require additional restraints beyond the traditional Nuclear Overhauser Effect (NOE) restraints. Several methods have been developed and this review focuses on paramagnetic relaxation enhancement (PRE). Important aspects of spin labeling, PRE measurements, structure calculations, and structural quality are discussed.

  19. In situ triaxial magnetic field compensation for the spin-exchange-relaxation-free atomic magnetometer.

    PubMed

    Fang, Jiancheng; Qin, Jie

    2012-10-01

    The spin-exchange-relaxation-free (SERF) atomic magnetometer is an ultra-high sensitivity magnetometer, but it must be operated in a magnetic field with strength less than about 10 nT. Magnetic field compensation is an effective way to shield the magnetic field, and this paper demonstrates an in situ triaxial magnetic field compensation system for operating the SERF atomic magnetometer. The proposed hardware is based on optical pumping, which uses some part of the SERF atomic magnetometer itself, and the compensation method is implemented by analyzing the dynamics of the atomic spin. The experimental setup for this compensation system is described, and with this configuration, a residual magnetic field of strength less than 2 nT (±0.38 nT in the x axis, ±0.43 nT in the y axis, and ±1.62 nT in the z axis) has been achieved after compensation. The SERF atomic magnetometer was then used to verify that the residual triaxial magnetic fields were coincident with what were achieved by the compensation system.

  20. Frequency-switching inversion-recovery for severely hyperfine-shifted NMR: evidence of asymmetric electron relaxation in high-spin Co(II).

    PubMed

    Riley, Erin A; Petros, Amy K; Smith, Karen Ann; Gibney, Brian R; Tierney, David L

    2006-12-11

    A new method for reliably measuring longitudinal relaxation rates for severely hyperfine-shifted NMR signals in aqueous solutions is presented. The method is illustrated for a well-defined cobalt tetracysteinate, with relevance to cobalt-substituted metalloproteins. The relaxation measurements are indicative of asymmetric electronic relaxation of the high-spin Co(II) ion.

  1. PREFACE: 13th International Conference on Muon Spin Rotation, Relaxation and Resonance

    NASA Astrophysics Data System (ADS)

    2014-12-01

    The 13th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2014) organized by the Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute in collaboration with the University of Zurich and the University of Fribourg, was held in Grindelwald, Switzerland from 1st to 6th June 2014. The conference provided a forum for researchers from around the world with interests in the applications of μSR to study a wide range of topics including condensed matter physics, materials and molecular sciences, chemistry and biology. Polarized muons provide a unique and versatile probe of matter, enabling studies at the atomic level of electronic structure and dynamics in a wide range of systems. The conference was the thirteenth in a series, which began in Rorschach in 1978 and it took place for the third time in Switzerland. The previous conferences were held in Cancun, Mexico (2011), Tsukuba, Japan (2008), Oxford, UK (2005), Williamsburg, USA (2002), Les Diablerets, Switzerland (1999), Nikko, Japan (1996), Maui, USA (1993), Oxford, UK (1990), Uppsala, Sweden (1986), Shimoda, Japan (1983), Vancouver, Canada (1980), and Rorschach, Switzerland (1978). These conference proceedings contain 67 refereed publications from presentations covering magnetism, superconductivity, chemistry, semiconductors, biophysics and techniques. The conference logo, displayed in the front pages of these proceedings, represents both the location of μSR2014 in the Alps and the muon-spin rotation technique. The silhouette represents the famous local mountains Eiger, Mönch and Jungfrau as drawn by the Swiss painter Ferdinand Hodler and the apple with arrow is at the same time a citation of the Wilhelm Tell legend and a remembrance of the key role played by the muon spin and the asymmetric muon decay (which for the highest positron energy has an apple like shape). More than 160 participants (including 32 registered as students and 13 as accompanying persons) from 19 countries

  2. Extension of the Rorschach-Hazlewood Theoretical Model for Spin-Lattice Relaxation in Biological Systems to Low Frequencies

    NASA Astrophysics Data System (ADS)

    Hackmann, Andreas; Ailion, David C.; Ganesan, Krishnamurthy; Laicher, Gernot; Goodrich, K. Craig; Cutillo, Antonio G.

    1996-02-01

    The water-biopolymer cross-relaxation model, proposed by H. E. Rorschach and C. F. Hazlewood (RH) [J. Magn. Reson.70,79 (1986)], explains the Larmor frequency dependence ofT1in many biological systems. However, the RH theory fails at low Larmor frequencies. In this paper, a more general version of the RH theory has been developed. This theory is valid at all frequencies. Use of the new expression for the spin-lattice relaxation rate (1/T1), earlier published experimental data in H2O/D2O bovine serum albumin, which had been measured over a wide frequency range (10 kHz to 100 MHz), were fitted over the entire frequency range. The agreement between theory and the experimental data is excellent. Theoretical expressions for the rotating-frame spin-lattice relaxation rate (1/T1ρ) were also obtained.

  3. Spin and phase relaxation dynamics in GaN and GaN/AlGaN quantum wells (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Gallart, Mathieu; Ziegler, Marc; Hönerlage, Bernd H.; Gilliot, Pierre; Feltin, Eric; Carlin, Jean-François; Butté, Raphaël.; Grandjean, Nicolas

    2015-09-01

    By performing time-resolved optical non-degenerate pump-probe experiments, we study the relaxation dynamics of spin-polarized excitons in wurtzite epitaxial GaN and in nitride nanostructures. Those materials are indeed promising candidates for spintronic applications because of their weak spin-orbit coupling and large exciton binding energy (~ 17 meV and ~ 26meV in bulk GaN, respectively). In epilayers, we show that the high density of dislocations increases dramatically the spin relaxation of electrons and holes through the defect assisted Elliott-Yafet mechanism. That makes the exciton dephasing time very short. In high quality GaN/AlGaN quantum wells, both the exciton-spin lifetime S and the exciton dephasing-time T2 were determined via pump-probe spectroscopy using polarized laser pulses and time-resolved four wave-mixing experiments. The evolution of both quantities with temperature shows that spin relaxation occurs in the motional narrowing regime up to 80 K. Above this threshold, the thermal energy becomes large enough for excitons to escape from the QW. Such measurements demonstrate that GaN-based heterostructures can reach a very high degree of control that was previously mostly restricted to conventional III-V semiconductors and more specifically to the arsenide family.

  4. Laterally localizing potential as a tool for controlling the electron spin relaxation time in GaAs quantum wells

    SciTech Connect

    Larionov, A. V.; Il’in, A. I.

    2013-12-15

    The coherent spin dynamics of electrons localized in a plane of GaAs quantum wells is studied experimentally by the application of an electrically controlled potential. The localizing potential is produced with the use of a metal gate with submicrometer windows deposited onto the sample surface. The photoinduced spin Kerr effect is used to study the electron spin lifetime as a function of the temperature, applied bias, and magnetic field for gates with different sets of windows. It is shown that, with an electrically controlled laterally localizing potential, it is possible to gradually change the electron spin lifetime from several hundreds of picoseconds to several tens of nanoseconds. The dependence of the electron spin relaxation time on the sizes of the lateral localization region is in good qualitative agreement with theoretical prediction.

  5. Spin-echo methods for the determination of 31P transverse relaxation times of the ATP NMR signals in vivo.

    PubMed

    Straubinger, K; Jung, W I; Bunse, M; Lutz, O; Küper, K; Dietze, G

    1994-01-01

    31P magnetic resonance spectroscopy (MRS) examinations of the calf muscles of healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the Hahn spin-echo and the frequency-selective spin-echo method. Additional measurements with the J-coupling refocused double echo are presented. The most reliable determination of T2 relaxation times is possible with the frequency-selective spin echo. The other methods yield substantially wrong results. Theoretical explanations are given how J-coupling and pulse-angle deviations affect the signals and therefore the T2 determinations. The calculations for a weakly coupled homonuclear AX spin system are shown because they demonstrate most of the relevant facts. In addition, some important results for a homonuclear AMX spin system, which the ATP is considered to be, are given.

  6. Determination of methyl 13C-15N dipolar couplings in peptides and proteins by three-dimensional and four-dimensional magic-angle spinning solid-state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Helmus, Jonathan J.; Nadaud, Philippe S.; Höfer, Nicole; Jaroniec, Christopher P.

    2008-02-01

    We describe three- and four-dimensional semiconstant-time transferred echo double resonance (SCT-TEDOR) magic-angle spinning solid-state nuclear magnetic resonance (NMR) experiments for the simultaneous measurement of multiple long-range N15-Cmethyl13 dipolar couplings in uniformly C13, N15-enriched peptides and proteins with high resolution and sensitivity. The methods take advantage of C13 spin topologies characteristic of the side-chain methyl groups in amino acids alanine, isoleucine, leucine, methionine, threonine, and valine to encode up to three distinct frequencies (N15-Cmethyl13 dipolar coupling, N15 chemical shift, and Cmethyl13 chemical shift) within a single SCT evolution period of initial duration ˜1/JCC1 (where JCC1≈35Hz, is the one-bond Cmethyl13-C13 J-coupling) while concurrently suppressing the modulation of NMR coherences due to C13-C13 and N15-C13 J-couplings and transverse relaxation. The SCT-TEDOR schemes offer several important advantages over previous methods of this type. First, significant (approximately twofold to threefold) gains in experimental sensitivity can be realized for weak N15-Cmethyl13 dipolar couplings (corresponding to structurally interesting, ˜3.5Å or longer, distances) and typical Cmethyl13 transverse relaxation rates. Second, the entire SCT evolution period can be used for Cmethyl13 and/or N15 frequency encoding, leading to increased spectral resolution with minimal additional coherence decay. Third, the experiments are inherently "methyl selective," which results in simplified NMR spectra and obviates the use of frequency-selective pulses or other spectral filtering techniques. Finally, the N15-C13 cross-peak buildup trajectories are purely dipolar in nature (i.e., not influenced by J-couplings or relaxation), which enables the straightforward extraction of N15-Cmethyl13 distances using an analytical model. The SCT-TEDOR experiments are demonstrated on a uniformly C13, N15-labeled peptide, N-acetyl-valine, and a 56

  7. Spin dynamics of the ordered dipolar-octupolar pseudospin-1/2 pyrochlore Nd2Zr2O7 probed by muon spin relaxation

    NASA Astrophysics Data System (ADS)

    Xu, J.; Balz, C.; Baines, C.; Luetkens, H.; Lake, B.

    2016-08-01

    We present a muon spin relaxation study on the Ising pyrochlore Nd2Zr2O7 which develops an "all-in-all-out" magnetic order below 0.4 K. At 20 mK, far below the ordering transition temperature, the zero-field muon spin relaxation spectra show no static features and can be well described by a dynamical Gaussian-broadened Gaussian Kubo-Toyabe function indicating strong fluctuations of the ordered state. The spectra of the paramagnetic state (below 4.2 K) reveal anomalously slow paramagnetic spin dynamics and show only a small difference with the spectra of the ordered state. We find that the fluctuation rate decreases with decreasing temperature and becomes nearly temperature independent below the transition temperature, indicating persistent slow spin dynamics in the ground state. The field distribution width shows a small but sudden increase at the transition temperature and then becomes almost constant. The spectra in applied longitudinal fields are well fitted by the conventional dynamical Gaussian Kubo-Toyabe function, which further supports the dynamical nature of the ground state. The fluctuation rate shows a peak as a function of external field which is associated with a field-induced spin-flip transition. The strong dynamics in the ordered state is attributed to the transverse coupling of the Ising spins introduced by the multipole interactions.

  8. Dynamics and supramolecular organization of the 1D spin transition polymeric chain compound [Fe(NH2trz)3](NO3)2. Muon spin relaxation.

    PubMed

    Garcia, Yann; Campbell, Stewart J; Lord, James S; Boland, Yves; Ksenofontov, Vadim; Gütlich, Philipp

    2007-09-27

    The thermal spin transition that occurs in the polymeric chain compound [Fe(NH(2)trz)3](NO3)2 above room temperature has been investigated by zero-field muon spin relaxation (microSR) over the temperature range approximately 8-402 K. The depolarization curves are best described by a Lorentzian and a Gaussian line that represent fast and slow components, respectively. The spin transition is associated with a hysteresis loop of width DeltaT = 34 K (T1/2 upward arrow = 346 K and T1/2 downward arrow = 312 K) that has been delineated by the temperature variation of the initial asymmetry parameter, in good agreement with previously published magnetic measurements. Zero-field and applied field (20-2000 Oe) microSR measurements show the presence of diamagnetic muon species and paramagnetic muonium radical species (A = 753 +/- 77 MHz) over the entire temperature range. Fast dynamics have been revealed in the high-spin state of [Fe(NH(2)trz)3](NO3)2 with the presence of a Gaussian relaxation mode that is mostly due to the dipolar interaction with static nuclear moments. This situation, where the muonium radicals are totally decoupled and not able to sense paramagnetic fluctuations, implies that the high-spin dynamics fall outside the muon time scale. Insights to the origin of the cooperative effects associated with the spin transition of [Fe(NH(2)trz)3](NO3)2 through muon implantation are presented.

  9. Theory of NMR 1 /T1 relaxation in a quantum spin nematic in an applied magnetic field

    NASA Astrophysics Data System (ADS)

    Smerald, Andrew; Shannon, Nic

    2016-05-01

    There is now strong theoretical evidence that a wide range of frustrated magnets should support quantum spin-nematic order in an applied magnetic field. Nonetheless, the fact that spin-nematic order does not break time-reversal symmetry makes it very difficult to detect in experiment. In this article, we continue the theme begun in Phys. Rev. B 88, 184430 (2013), 10.1103/PhysRevB.88.184430, of exploring how spin-nematic order reveals itself in the spectrum of spin excitations. Building on an earlier analysis of inelastic neutron scattering [Phys. Rev. B 91, 174402 (2015), 10.1103/PhysRevB.91.174402], we show how the NMR 1 /T1 relaxation rate could be used to identify a spin-nematic state in an applied magnetic field. We emphasize the characteristic universal features of 1 /T1 using a symmetry-based description of the spin-nematic order parameter and its fluctuations. Turning to the specific case of spin-1/2 frustrated ferromagnets, we show that the signal from competing spin-wave excitations can be suppressed through a judicious choice of nuclear site and field direction. As a worked example, we show how 31P NMR in the square lattice frustrated ferromagnet BaCdVO (PO4)2 is sensitive to spin-nematic order.

  10. Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3(NIT(C6H4OPh))]: A μ{sup +} spin relaxation study

    SciTech Connect

    Arosio, Paolo Orsini, Francesco; Corti, Maurizio; Mariani, Manuel; Bogani, Lapo; Caneschi, Andrea; Lago, Jorge; Lascialfari, Alessandro

    2015-05-07

    The spin dynamics of the molecular magnetic chain [Dy(hfac){sub 3}(NIT(C{sub 6}H{sub 4}OPh))] were investigated by means of the Muon Spin Relaxation (μ{sup +}SR) technique. This system consists of a magnetic lattice of alternating Dy(III) ions and radical spins, and exhibits single-chain-magnet behavior. The magnetic properties of [Dy(hfac){sub 3}(NIT(C{sub 6}H{sub 4}OPh))] have been studied by measuring the magnetization vs. temperature at different applied magnetic fields (H = 5, 3500, and 16500 Oe) and by performing μ{sup +}SR experiments vs. temperature in zero field and in a longitudinal applied magnetic field H = 3500 Oe. The muon asymmetry P(t) was fitted by the sum of three components, two stretched-exponential decays with fast and intermediate relaxation times, and a third slow exponential decay. The temperature dependence of the spin dynamics has been determined by analyzing the muon longitudinal relaxation rate λ{sub interm}(T), associated with the intermediate relaxing component. The experimental λ{sub interm}(T) data were fitted with a corrected phenomenological Bloembergen-Purcell-Pound law by using a distribution of thermally activated correlation times, which average to τ = τ{sub 0} exp(Δ/k{sub B}T), corresponding to a distribution of energy barriers Δ. The correlation times can be associated with the spin freezing that occurs when the system condenses in the ground state.

  11. Radiofrequency (RF) Coil Impacts the Value and Reproducibility of Cartilage Spin-Spin (T2) Relaxation Time Measurements

    PubMed Central

    Dardzinski, BJ; Schneider, E

    2013-01-01

    Introduction T2 (spin-spin) relaxation time is frequently used for compositional assessment of articular cartilage. However little is known about the influence of MR system components on these measurements. The reproducibility and range of cartilage T2 values were evaluated using different extremity radiofrequency (RF) coils with potential differences in flip angle uniformity and SNR. Method Ten knees underwent 3 Tesla MR exams using RF coils with different signal-to-noise (SNR): quadrature transmit/receive (QTR); quadrature transmit/eight-channel phased-array receive (QT8PAR). Each knee was scanned twice per coil (4 exams total). T2 values were calculated for the central medial and lateral femoral (cMF, cLF) and medial and lateral tibial (MT, LT) cartilage. Results The flip angle varied across a central 40mm diameter region-of-interest of each coil by <1.5%. However SNR was significantly higher using QT8PAR than QTR (p<0.001). T2 values for cMF (50.7msec/45.9msec) and MT (48.2msec/41.6msec) were significantly longer with QT8PAR than QTR (p<0.05). T2 reproducibility was improved using QT8PAR for cMF and cLF (4.8%/5.8% and 4.1%/6.5%; p<0.001), similar for LT (3.8%/3.6%; p=1.0), and worse for MT (3.7%/3.3%; p<0.001). T2 varied spatially, with cLF having the longest (52.0msec) and the LT having the shortest (40.6msec) values. All deep cartilage had significantly longer, and less variable, T2 values using QT8PAR (higher SNR; p<0.03). Conclusions SNR varied spatially depending upon coil, but refocusing flip angle did not. With higher SNR, significantly longer T2 values were measured for deep (all plates) and global (MT, cMF) cartilage. T2 values varied by depth and plate, in agreement with prior studies. PMID:23376528

  12. Spin-lattice relaxation study of the methyl proton dynamics in solid 9,10-dimethyltriptycene (DMT).

    PubMed

    Piślewski, N; Tritt-Goc, J; Bielejewski, M; Rachocki, A; Ratajczyk, T; Szymański, S

    2009-06-01

    Proton spin-lattice relaxation studies are performed for powder samples of 9,10-dimethyltriptycene (DMT) and its isotopomer DMT-d(12) in which all the non-methyl protons in the molecule are replaced by deuterons. The relaxation data are interpreted in terms of the conventional relaxation theory based on the random jump model in which the Pauli correlations between the relevant spin and torsional states are discarded. The Arrhenius activation energies, obtained from the relaxation data, 25.3 and 24.8 kJ mol(-1) for DMT and DMT-d(12), respectively, are very high as for the methyl groups. The validity of the jump model in the present case is considered from the perspective of Haupt theory in which the Pauli principle is explicitly invoked. To this purpose, the dynamic quantities entering the Haupt model are reinterpreted in the spirit of the damped quantum rotation (DQR) approach introduced recently for the purpose of NMR lineshape studies of hindered molecular rotators. Theoretical modelling of the relevant methyl group dynamics, based on the DQR theory, was performed. From these calculations it is inferred that direct assessments of the torsional barrier heights, based on the Arrhenius activation energies extracted from relaxation data, should be treated with caution.

  13. The influence of oxygen-17 enriched oxygen-donor ligands on the electronic spin relaxation behaviour of paramagnetic metal ions

    NASA Astrophysics Data System (ADS)

    Wells, Gregg B.; Yim, Moon B.; Makinen, Marvin W.

    Continuous wave microwave power saturation of high-spin paramagnetic metalloprotein complexes of Co2+ and Fe3+ showed that the value of the saturation parameter P1/2 is influenced by the coordination of oxygen-17 enriched water to the metal ion. No change was observed for H218O or 2H2O. Pulse saturation and recovery of paramagnetic high-spin Fe3+ heme proteins identified a fast relaxation component sensitive to isotopic oxygen-17 composition that was assigned to the process of spectral diffusion. It is shown that the change in relaxation time for spectral diffusion can alter the (apparent) spin-lattice relaxation to account for the observed changes in continuous wave microwave power saturation experiments. These changes are shown to correlate with alterations in the extent of covalency between the metal ion and oxygen-donor ligand. The experimental results provide a basis for use of continuous wave microwave saturation to identify the presence of oxygen-donor ligands within the inner coordination shell of high-spin Co2+ or Fe3+ in metalloprotein and small molecule complexes and to qualitatively assess the extent of covalency between the metal ion and the oxygen-donor ligand.

  14. Molecular Level Insights on Collagen-Polyphenols Interaction Using Spin-Relaxation and Saturation Transfer Difference NMR.

    PubMed

    Reddy, R Ravikanth; Phani Kumar, Bandaru V N; Shanmugam, Ganesh; Madhan, Balaraman; Mandal, Asit B

    2015-11-01

    Interaction of small molecules with collagen has far reaching consequences in biological and industrial processes. The interaction between collagen and selected polyphenols, viz., gallic acid (GA), pyrogallol (PG), catechin (CA), and epigallocatechin gallate (EGCG), has been investigated by various solution NMR measurements, viz., (1)H and (13)C chemical shifts (δH and δC), (1)H nonselective spin-lattice relaxation times (T1NS) and selective spin-lattice relaxation times (T1SEL), as well as spin-spin relaxation times (T2). Furthermore, we have employed saturation transfer difference (STD) NMR method to monitor the site of GA, CA, PG, and EGCG which are in close proximity to collagen. It is found that -COOH group of GA provides an important contribution for the interaction of GA with collagen, as evidenced from (13)C analysis, while PG, which is devoid of -COOH group in comparison to GA, does not show any significant interaction with collagen. STD NMR data indicates that the resonances of A-ring (H2', H5' and H6') and C-ring (H6 and H8) protons of CA, and A-ring (H2' and H6'), C-ring (H6 and H8), and D-ring (H2″and H6″) protons of EGCG persist in the spectra, demonstrating that these protons are in spatial proximity to collagen, which is further validated by independent proton spin-relaxation measurement and analysis. The selective (1)H T1 measurements of polyphenols in the presence of protein at various concentrations have enabled us to determine their binding affinities with collagen. EGCG exhibits high binding affinity with collagen followed by CA, GA, and PG. Further, NMR results propose that presence of gallic acid moiety in a small molecule increases its affinity with collagen. Our experimental findings provide molecular insights on the binding of collagen and plant polyphenols. PMID:26447653

  15. Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe_{2}O_{6}: NMR and Muon Spin Relaxation Studies.

    PubMed

    Khuntia, P; Bert, F; Mendels, P; Koteswararao, B; Mahajan, A V; Baenitz, M; Chou, F C; Baines, C; Amato, A; Furukawa, Y

    2016-03-11

    PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation. PMID:27015508

  16. Spin liquid state in the 3D frustrated antiferromagnet PbCuTe2O6: NMR and muon spin relaxation studies

    DOE PAGES

    Khuntia, P.; Bert, F.; Mendels, P.; Koteswararao, B.; Mahajan, A. V.; Baenitz, M.; Chou, F. C.; Baines, C.; Amato, A.; Furukawa, Y.

    2016-03-11

    In this study, PbCuTe2O6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneousmore » magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less

  17. Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe_{2}O_{6}: NMR and Muon Spin Relaxation Studies.

    PubMed

    Khuntia, P; Bert, F; Mendels, P; Koteswararao, B; Mahajan, A V; Baenitz, M; Chou, F C; Baines, C; Amato, A; Furukawa, Y

    2016-03-11

    PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.

  18. Resonantly enhanced spin-lattice relaxation of Mn2 + ions in diluted magnetic (Zn,Mn)Se/(Zn,Be)Se quantum wells

    NASA Astrophysics Data System (ADS)

    Debus, J.; Ivanov, V. Yu.; Ryabchenko, S. M.; Yakovlev, D. R.; Maksimov, A. A.; Semenov, Yu. G.; Braukmann, D.; Rautert, J.; Löw, U.; Godlewski, M.; Waag, A.; Bayer, M.

    2016-05-01

    The dynamics of spin-lattice relaxation in the magnetic Mn2 + ion system of (Zn,Mn)Se/(Zn,Be)Se quantum-well structures are studied using optical methods. Pronounced cusps are found in the giant Zeeman shift of the quantum-well exciton photoluminescence at specific magnetic fields below 10 T, when the Mn spin system is heated by photogenerated carriers. The spin-lattice relaxation time of the Mn ions is resonantly accelerated at the cusp magnetic fields. Our theoretical analysis demonstrates that a cusp occurs at a spin-level mixing of single Mn2 + ions and a quick-relaxing cluster of nearest-neighbor Mn ions, which can be described as intrinsic cross-relaxation resonance within the Mn spin system.

  19. Phase-coherent transport and spin relaxation in InAs nanowires grown by molecule beam epitaxy

    SciTech Connect

    Wang, L. B.; Guo, J. K.; Kang, N. E-mail: hqxu@pku.edu.cn; Li, Sen; Fan, Dingxun; Pan, Dong; Zhao, Jianhua; Xu, H. Q. E-mail: hqxu@pku.edu.cn

    2015-04-27

    We report low-temperature magnetotransport studies of individual InAs nanowires grown by molecule beam epitaxy. At low magnetic fields, the magnetoconductance characteristics exhibit a crossover between weak antilocalization and weak localization by changing either the gate voltage or the temperature. The observed crossover behavior can be well described in terms of relative scales of the transport characteristic lengths extracted based on the quasi-one-dimensional theory of weak localization in the presence of spin-orbit interaction. The spin relaxation length extracted from the magnetoconductance data is found to be in the range of 80–100 nm, indicating the presence of strong spin-orbit coupling in the InAs nanowires. Moreover, the amplitude of universal conductance fluctuations in the nanowires is found to be suppressed at low temperatures due to the presence of strong spin-orbit scattering.

  20. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2

    DOE PAGES

    Yang, Luyi; Sinitsyn, Nikolai A.; Chen, Weibing; Yuan, Jiangtan; Zhang, Jing; Lou, Jun; Crooker, Scott  A.

    2015-08-03

    The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin–valley physics. Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments PL timescales are necessarily constrained by short-lived (3–100 ps) electron–hole recombination9, 10. Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage. Here we directly measure the coupled spin–valley dynamics in electron-doped MoS2 and WS2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3 ns atmore » 5 K (2-3 orders of magnitude longer than typical exciton recombination times). In contrast with conventional III–V or II–VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin–valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin–orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.« less

  1. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2

    SciTech Connect

    Yang, Luyi; Sinitsyn, Nikolai A.; Chen, Weibing; Yuan, Jiangtan; Zhang, Jing; Lou, Jun; Crooker, Scott  A.

    2015-08-03

    The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin–valley physics. Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments PL timescales are necessarily constrained by short-lived (3–100 ps) electron–hole recombination9, 10. Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage. Here we directly measure the coupled spin–valley dynamics in electron-doped MoS2 and WS2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3 ns at 5 K (2-3 orders of magnitude longer than typical exciton recombination times). In contrast with conventional III–V or II–VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin–valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin–orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.

  2. Spin-exchange relaxation-free magnetometer with nearly parallel pump and probe beams

    DOE PAGES

    Karaulanov, Todor; Savukov, Igor; Kim, Young Jin

    2016-03-22

    We constructed a spin-exchange relaxation-free (SERF) magnetometer with a small angle between the pump and probe beams facilitating a multi-channel design with a flat pancake cell. This configuration provides almost complete overlap of the beams in the cell, and prevents the pump beam from entering the probe detection channel. By coupling the lasers in multi-mode fibers, without an optical isolator or field modulation, we demonstrate a sensitivity of 10 fTmore » $$/\\sqrt{\\text{Hz}}$$ for frequencies between 10 Hz and 100 Hz. In addition to the experimental study of sensitivity, we present a theoretical analysis of SERF magnetometer response to magnetic fields for small-angle and parallel-beam configurations, and show that at optimal DC offset fields the magnetometer response is comparable to that in the orthogonal-beam configuration. Based on the analysis, we also derive fundamental and probe-limited sensitivities for the arbitrary non-orthogonal geometry. The expected practical and fundamental sensitivities are of the same order as those in the orthogonal geometry. As a result, we anticipate that our design will be useful for magnetoencephalography (MEG) and magnetocardiography (MCG) applications.« less

  3. Suppression of vapor cell temperature error for spin-exchange-relaxation-free magnetometer

    SciTech Connect

    Lu, Jixi Qian, Zheng; Fang, Jiancheng; Quan, Wei

    2015-08-15

    This paper presents a method to reduce the vapor cell temperature error of the spin-exchange-relaxation-free (SERF) magnetometer. The fluctuation of cell temperature can induce variations of the optical rotation angle, resulting in a scale factor error of the SERF magnetometer. In order to suppress this error, we employ the variation of the probe beam absorption to offset the variation of the optical rotation angle. The theoretical discussion of our method indicates that the scale factor error introduced by the fluctuation of the cell temperature could be suppressed by setting the optical depth close to one. In our experiment, we adjust the probe frequency to obtain various optical depths and then measure the variation of scale factor with respect to the corresponding cell temperature changes. Our experimental results show a good agreement with our theoretical analysis. Under our experimental condition, the error has been reduced significantly compared with those when the probe wavelength is adjusted to maximize the probe signal. The cost of this method is the reduction of the scale factor of the magnetometer. However, according to our analysis, it only has minor effect on the sensitivity under proper operating parameters.

  4. a Spin Relaxation Model for the Moessbauer Spectra of Barium Tin

    NASA Astrophysics Data System (ADS)

    Irwin, George Michael

    The stochastic relaxation theory of Anderson and Sack is applied to the Mossbauer spectra of seven samples of BaSn_{rm x}Ti _{rm 2-x}Fe _4O_{11} with compositions x = 0.0, 0.4, 0.6, 0.8, 1.2, 1.6, and 2.0. The spectra were obtained at room temperature and in the temperature range 20 K to 170 K. The broad, low temperature spectra were analysed using least square fitting to a simple model for Fe^{3+} in which the ionic moment is subject to a molecular field and a perpendicular random field which induces transitions between spin states. The resulting fits rival the results of analyses on similar systems using static hyperfine field distributions while requiring only two free parameters to mimic the temperature dependence of the spectral lineshapes. The results verify a magnetic double transition in the sample with x = 0.0 which disappears as Sn is added, but suggests that the samples with x = 1.2, 1.6, and 2.0 also show a double transition that has not been observed using other methods.

  5. Spin-lattice relaxation in p-type gallium arsenide single crystals

    NASA Astrophysics Data System (ADS)

    Zerrouati, K.; Fabre, F.; Bacquet, G.; Bandet, J.; Frandon, J.; Lampel, G.; Paget, D.

    1988-01-01

    An optical-pumping technique is used to measure the spin-relaxation time of photogenerated conduction electrons in several p-type GaAs single crystals doped with various amounts of acceptors in the 1.7-300 K temperature range. Our experimental results are compared with those of the literature and with the predictions of the existing theoretical calculations. From about 10 K, the Bir-Aronov-Pikus (BAP) mechanism is found to be relevant for moderately doped (1017-1018 cm-3), up to about 150 K, or degenerate (up to 300 K) semiconductors, using the electronic temperature, deduced from the luminescence spectra, rather than the sample temperature. The D'yakonov-Perel' (DP) process was found to be active above 200 K for moderately doped samples and from about 80 K to room temperature for samples doped in the (1.6-6)×1016-cm-3 acceptor-concentration range. Our original results obtained at liquid-helium temperatures at whatever the doping level cannot be explained either by the DP mechanism or by the BAP process.

  6. Spin-exchange relaxation-free magnetometer with nearly parallel pump and probe beams

    NASA Astrophysics Data System (ADS)

    Karaulanov, Todor; Savukov, Igor; Kim, Young Jin

    2016-05-01

    We constructed a spin-exchange relaxation-free (SERF) magnetometer with a small angle between the pump and probe beams facilitating a multi-channel design with a flat pancake cell. This configuration provides almost complete overlap of the beams in the cell, and prevents the pump beam from entering the probe detection channel. By coupling the lasers in multi-mode fibers, without an optical isolator or field modulation, we demonstrate a sensitivity of 10 f T/\\sqrt{\\text{Hz}} for frequencies between 10 Hz and 100 Hz. In addition to the experimental study of sensitivity, we present a theoretical analysis of SERF magnetometer response to magnetic fields for small-angle and parallel-beam configurations, and show that at optimal DC offset fields the magnetometer response is comparable to that in the orthogonal-beam configuration. Based on the analysis, we also derive fundamental and probe-limited sensitivities for the arbitrary non-orthogonal geometry. The expected practical and fundamental sensitivities are of the same order as those in the orthogonal geometry. We anticipate that our design will be useful for magnetoencephalography (MEG) and magnetocardiography (MCG) applications.

  7. Suppression of vapor cell temperature error for spin-exchange-relaxation-free magnetometer.

    PubMed

    Lu, Jixi; Qian, Zheng; Fang, Jiancheng; Quan, Wei

    2015-08-01

    This paper presents a method to reduce the vapor cell temperature error of the spin-exchange-relaxation-free (SERF) magnetometer. The fluctuation of cell temperature can induce variations of the optical rotation angle, resulting in a scale factor error of the SERF magnetometer. In order to suppress this error, we employ the variation of the probe beam absorption to offset the variation of the optical rotation angle. The theoretical discussion of our method indicates that the scale factor error introduced by the fluctuation of the cell temperature could be suppressed by setting the optical depth close to one. In our experiment, we adjust the probe frequency to obtain various optical depths and then measure the variation of scale factor with respect to the corresponding cell temperature changes. Our experimental results show a good agreement with our theoretical analysis. Under our experimental condition, the error has been reduced significantly compared with those when the probe wavelength is adjusted to maximize the probe signal. The cost of this method is the reduction of the scale factor of the magnetometer. However, according to our analysis, it only has minor effect on the sensitivity under proper operating parameters.

  8. Dynamics of 4-oxo-TEMPO-d16-15N nitroxide-propylene glycol system studied by ESR and ESE in liquid and glassy state in temperature range 10-295 K

    NASA Astrophysics Data System (ADS)

    Goslar, Janina; Hoffmann, Stanislaw K.; Lijewski, Stefan

    2016-08-01

    ESR spectra and electron spin relaxation of nitroxide radical in 4-oxo-TEMPO-d16-15N in propylene glycol were studied at X-band in the temperature range 10-295 K. The spin-lattice relaxation in the liquid viscous state determined from the resonance line shape is governed by three mechanisms occurring during isotropic molecular reorientations. In the glassy state below 200 K the spin-lattice relaxation, phase relaxation and electron spin echo envelope modulations (ESEEM) were studied by pulse spin echo technique using 2-pulse and 3-pulse induced signals. Electron spin-lattice relaxation is governed by a single non-phonon relaxation process produced by localized oscillators of energy 76 cm-1. Electron spin dephasing is dominated by a molecular motion producing a resonance-type peak in the temperature dependence of the dephasing rate around 120 K. The origin of the peak is discussed and a simple method for the peak shape analysis is proposed, which gives the activation energy of a thermally activated motion Ea = 7.8 kJ/mol and correlation time τ0 = 10-8 s. The spin echo amplitude is strongly modulated and FT spectrum contains a doublet of lines centered around the 2D nuclei Zeeman frequency. The splitting into the doublet is discussed as due to a weak hyperfine coupling of nitroxide unpaired electron with deuterium of reorienting CD3 groups.

  9. Spin relaxation and linear-in-electric-field frequency shift in an arbitrary, time-independent magnetic field

    SciTech Connect

    Clayton, Steven Michael

    2010-12-03

    A method is presented to calculate the spin relaxation times T{sub 1}, T{sub 2} due to a nonuniform magnetic field, and the linear-in-electric-field precession frequency shift {delta}{omega}{sub E} when an electric field is present, in the diffusion approximation for spins confined to a rectangular cell. It is found that the rectangular cell geometry admits of a general result for T{sub 1}, T{sub 2}, and {delta}{omega}{sub E} in terms of the spatial cosine-transform components of the magnetic field.

  10. Muon spin relaxation study of Zr(H2PO4)(PO4).2H2O.

    PubMed

    Clayden, Nigel J; Cottrell, Stephen P

    2006-07-14

    Muon spin relaxation has been used to study the muon dynamics in the layered zirconium phosphate Zr(H(2)PO(4))(PO(4)).2H(2)O as a function of temperature. Radiofrequency decoupling was used to establish the origin of the local dipolar field as coupling with (1)H spins. Muons were trapped at two sites, one identified as HMuO and the other consistent with PO-Mu on the basis of their zero-field second moments. Although a small decrease in the local nuclear dipolar field was seen with temperature, the muons remained essentially static over the temperature range 20-300 K.

  11. Gd3+ spin-lattice relaxation via multi-band conduction electrons in Y(1-x)Gd(x)In3: an electron spin resonance study.

    PubMed

    Cabrera-Baez, M; Iwamoto, W; Magnavita, E T; Osorio-Guillén, J M; Ribeiro, R A; Avila, M A; Rettori, C

    2014-04-30

    Interest in the electronic structure of the intermetallic compound YIn3 has been renewed with the recent discovery of superconductivity at T ∼ 1 K, which may be filamentary in nature. In this work we perform electron spin resonance (ESR) experiments on Gd(3+) doped YIn3 (Y1-xGdxIn3; 0.001 ⪅ x ⩽̸ 0.08), showing that the spin-lattice relaxation of the Gd(3+) ions, due to the exchange interaction between the Gd(3+) localized magnetic moment and the conduction electrons (ce), is processed via the presence of s-, p- and d-type ce at the YIn3 Fermi level. These findings are revealed by the Gd(3+) concentration dependence of the Korringa-like relaxation rate d(ΔH)/dT and g-shift (Δg = g - 1.993), that display bottleneck relaxation behavior for the s-electrons and unbottleneck behavior for the p- and d-electrons. The Korringa-like relaxation rates vary from 22(2) Oe/K for x ⪅ 0.001 to 8(2) Oe/K for x = 0.08 and the g-shift values change, respectively, from a positive Δg = +0.047(10) to a negative Δg = -0.008(4). Analysis in terms of a three-band ce model allows the extraction of the corresponding exchange interaction parameters Jfs, Jfp and Jfd.

  12. PREFACE: 13th International Conference on Muon Spin Rotation, Relaxation and Resonance

    NASA Astrophysics Data System (ADS)

    2014-12-01

    The 13th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2014) organized by the Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute in collaboration with the University of Zurich and the University of Fribourg, was held in Grindelwald, Switzerland from 1st to 6th June 2014. The conference provided a forum for researchers from around the world with interests in the applications of μSR to study a wide range of topics including condensed matter physics, materials and molecular sciences, chemistry and biology. Polarized muons provide a unique and versatile probe of matter, enabling studies at the atomic level of electronic structure and dynamics in a wide range of systems. The conference was the thirteenth in a series, which began in Rorschach in 1978 and it took place for the third time in Switzerland. The previous conferences were held in Cancun, Mexico (2011), Tsukuba, Japan (2008), Oxford, UK (2005), Williamsburg, USA (2002), Les Diablerets, Switzerland (1999), Nikko, Japan (1996), Maui, USA (1993), Oxford, UK (1990), Uppsala, Sweden (1986), Shimoda, Japan (1983), Vancouver, Canada (1980), and Rorschach, Switzerland (1978). These conference proceedings contain 67 refereed publications from presentations covering magnetism, superconductivity, chemistry, semiconductors, biophysics and techniques. The conference logo, displayed in the front pages of these proceedings, represents both the location of μSR2014 in the Alps and the muon-spin rotation technique. The silhouette represents the famous local mountains Eiger, Mönch and Jungfrau as drawn by the Swiss painter Ferdinand Hodler and the apple with arrow is at the same time a citation of the Wilhelm Tell legend and a remembrance of the key role played by the muon spin and the asymmetric muon decay (which for the highest positron energy has an apple like shape). More than 160 participants (including 32 registered as students and 13 as accompanying persons) from 19 countries

  13. Lattice dynamics, phase transitions and spin relaxation in [Fe(C5H5)2] PF6

    NASA Astrophysics Data System (ADS)

    Herber, R. H.; Felner, I.; Nowik, I.

    2016-12-01

    The organometallic compound ferrocenium hexafluorophosphate, [Fe(C5H5)2] PF6, has been studied by Mössbauer spectroscopy in the past, mainly to determine the crystal structure at high temperatures. Here we present studies at 95 K to 305 K and analyze the spectra in terms of spin relaxation theory which yields accurately the hyperfine interaction parameters and the spin-spin and spin-lattice relaxation rates in this paramagnetic compound. The spectral area under the resonance curve yields the recoil free fraction and thus the mean square of the vibration amplitude . One observes a large discontinuity in the slope of versus T at ˜210 K, indicative of a phase transition. The analysis of the spectra proves that the quadrupole interaction is small but certainly negative, ½e2qQ = -0.12(2) mm/s, and causes the asymmetry observed in the spectra. The detailed analysis yields also, for the first time, the fluctuating effective magnetic hyperfine field, H eff = 180(50) kOe.

  14. Phospholipid bilayer relaxation dynamics as revealed by the pulsed electron-electron double resonance of spin labels

    NASA Astrophysics Data System (ADS)

    Syryamina, V. N.; Dzuba, S. A.

    2012-10-01

    Electron paramagnetic resonance (EPR) spectroscopy in the form of pulsed electron-electron double resonance (ELDOR) was applied to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) phospholipid bilayers containing lipids that were spin-labeled at different carbon positions along the lipid acyl chain. Pulsed ELDOR detects motionally induced spin flips of nitrogen nuclei in the nitroxide spin labels, which manifests itself as magnetization transfer (MT) in the nitroxide EPR spectrum. The MT effect was observed over a wide temperature range (100-225 K) on a microsecond time scale. In line with a previous study on molecular glasses [N. P. Isaev and S. A. Dzuba, J. Chem. Phys. 135, 094508 (2011), 10.1063/1.3633241], the motions that induce MT effect were suggested to have the same nature as those in dielectric secondary (β) Johari-Goldstein fast relaxation. The results were compared with literature dielectric relaxation data for POPC bilayers, revealing some common features. Molecular motions resulting in MT are faster for deeper spin labels in the membrane interior. The addition of cholesterol to the bilayer suppresses the lipid motions near the steroid nucleus and accelerates the lipid motions beyond the steroid nucleus, in the bilayer interior. This finding was attributed to the lipid acyl chains being more ordered near the steroid nucleus and less ordered in the bilayer interior. The motions are absent in dry lipids, indicating that the motions are determined by intermolecular interactions in the bilayer.

  15. On the origin of the two thermally driven relaxations in diluted spin ice Dy(1.6)Y(0.4)Ti2O7.

    PubMed

    Xing, Hui; Guo, Hanjie; Feng, Chunmu; Xu, Zhu-An; Zeng, Hao

    2013-01-30

    We report quantitative analysis of the ac susceptibility of the diluted spin ice compound Dy(1.6)Y(0.4)Ti(2)O(7), by fitting the frequency spectra of the two observed relaxation modes with a double Cole-Cole formula. Our results suggest that both modes are thermally activated, with the same intrinsic frequency, but different activation barriers. We propose that these thermally activated relaxation modes can be attributed to correlated spin clusters.

  16. Static magnetic ordering of CeCu2.1Si2 found by muon spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Schone, H. E.; Kempton, J. R.; Stronach, C. E.; Barth, S.; Gygax, F. N.; Hitti, B.; Schenck, A.

    1988-01-01

    Zero- and longitudinal-field muon spin relaxation measurements on a polycrystal sample of a heavy fermion superconductor CeCu2.1 Si2 (T(c) = 0.7 K) have revealed an onset of static magnetic ordering below T approximately 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1 micro-B per formula unit.

  17. Low-relaxation spin waves in laser-molecular-beam epitaxy grown nanosized yttrium iron garnet films

    NASA Astrophysics Data System (ADS)

    Lutsev, L. V.; Korovin, A. M.; Bursian, V. E.; Gastev, S. V.; Fedorov, V. V.; Suturin, S. M.; Sokolov, N. S.

    2016-05-01

    Synthesis of nanosized yttrium iron garnet (Y3Fe5O12, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10-5. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

  18. Spin-lattice relaxation of ligand nuclei in slowly reorienting paramagnetic complexes in the electronic doublet spin state ( S = {1}/{2}). A theoretical approach for strongly coupled two-spin systems

    NASA Astrophysics Data System (ADS)

    Benetis, Nikolas P.

    In this paper a general theory for treating the spin-lattice relaxation of a ligand nucleus (denoted by I) is derived for a metal complex in a doublet electron spin state ( S = {1}/{2}). The dipole-dipole SI interaction is treated for the case where the electron spin is also strongly coupled to the metal nucleus K. The SK interaction considered here is the hyperfine coupling, both scalar (SC) and dipolar (DD). The present theory is valid for slowly reorienting complexes in solution and can, furthermore, incorporate relaxation effects of the electron spin S, and the metal nucleus K due to processes which are faster than, and independent of, reorientation, i.e., for processes that fulfil the strong narrowing conditions. The effects of chemical exchange of the ligands and of anisotropic reorientation of the complex are also studied. Together with our previous studies of paramagnetic complexes with electron spin S ≧ 1, that have been recently reviewed by J. Kowalewski, L. Nordenskiöld, N. Benetis, and P. O. Westlund, ( Prog. NMR Spectrosc.17, 141 (1985)), the present work completes the elementary relaxation features of ligand nuclei of metal complexes in the slow motional regime. The present theory is shown to be more general than the theory of Bertini and co-workers ( J. Magn. Reson.59 , 213 (1984)), which can be obtained as a limit of the present approach by decoupling the reorientation from the motions of the S-K two spin system. The treatment of a strongly coupled two-spin system is emphasized since it provides a necessary step to the treatment of the relaxation of paramagnetic doublets.

  19. Asymmetric simultaneous phase-inversion cross-polarization in solid-state MAS NMR: Relaxing selective polarization transfer condition between two dilute spins

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengfeng; Fu, Riqiang; Li, Jianping; Yang, Jun

    2014-05-01

    Double cross polarization (DCP) has been widely used for heteronuclear polarization transfer between 13C and 15N in solid-state magic-angle spinning (MAS) NMR. However, DCP is such sensitive to experimental settings that small variations or deviations in RF fields would deteriorate its efficiency. Here, we report on asymmetric simultaneous phase-inversion cross polarization (referred as aSPICP) for selective polarization transfer between low-γ 13C and 15N spins. We have demonstrated through simulations and experiments using biological solids that the asymmetric duration in the simultaneous phase-inversion cross polarization scheme leads to efficient polarization transfer between 13C and 15N even with large chemical shift anisotropies in the presence of B1 field variations or mismatch of the Hartmann-Hahn conditions. This could be very useful in the aspect of long-duration experiments for membrane protein studies at high fields.

  20. Nonequilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar-coupled spin-glass LiHo0.5Er0.5F4

    NASA Astrophysics Data System (ADS)

    Piatek, J. O.; Kovacevic, I.; Babkevich, P.; Dalla Piazza, B.; Neithardt, S.; Gavilano, J.; Krämer, K. W.; Rønnow, H. M.

    2014-11-01

    We present a study of the model spin-glass LiHo0.5Er0.5F4 using simultaneous ac susceptibility, magnetization, and magnetocaloric effect measurements along with small angle neutron scattering (SANS) at sub-Kelvin temperatures. All measured bulk quantities reveal hysteretic behavior when the field is applied along the crystallographic c axis. Furthermore, avalanchelike relaxation is observed in a static field after ramping from the zero-field-cooled state up to 200-300 Oe. SANS measurements are employed to track the microscopic spin reconfiguration throughout both the hysteresis loop and the related relaxation. Comparing the SANS data to inhomogeneous mean-field calculations performed on a box of one million unit cells provides a real-space picture of the spin configuration. We discover that the avalanche is being driven by released Zeeman energy, which heats the sample and creates positive feedback, continuing the avalanche. The combination of SANS and mean-field simulations reveal that the conventional distribution of cluster sizes is replaced by one with a depletion of intermediate cluster sizes for much of the hysteresis loop.

  1. Measurement of sample temperatures under magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder

    PubMed Central

    Thurber, Kent R.; Tycko, Robert

    2009-01-01

    Accurate determination of sample temperatures in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) can be problematic, particularly because frictional heating and heating by radio-frequency irradiation can make the internal sample temperature significantly different from the temperature outside the MAS rotor. This paper demonstrates the use of 79Br chemical shifts and spin-lattice relaxation rates in KBr powder as temperature-dependent parameters for the determination of internal sample temperatures. Advantages of this method include high signal-to-noise, proximity of the 79Br NMR frequency to that of 13C, applicability from 20 K to 320 K or higher, and simultaneity with adjustment of the MAS axis direction. We show that spin-lattice relaxation in KBr is driven by a quadrupolar mechanism. We demonstrate a simple approach to including KBr powder in hydrated samples, such as biological membrane samples, hydrated amyloid fibrils, and hydrated microcrystalline proteins, that allows direct assessment of the effects of frictional and radio-frequency heating under experimentally relevant conditions. PMID:18930418

  2. Electron spin relaxation times and rapid scan EPR imaging of pH-sensitive amino-substituted trityl radicals.

    PubMed

    Elajaili, Hanan B; Biller, Joshua R; Tseitlin, Mark; Dhimitruka, Ilirian; Khramtsov, Valery V; Eaton, Sandra S; Eaton, Gareth R

    2015-04-01

    Carboxy-substituted trityl (triarylmethyl) radicals are valuable in vivo probes because of their stability, narrow lines, and sensitivity of their spectroscopic properties to oxygen. Amino-substituted trityl radicals have the potential to monitor pH in vivo, and the suitability for this application depends on spectral properties. Electron spin relaxation times T1 and T2 were measured at X-band for the protonated and deprotonated forms of two amino-substituted triarylmethyl radicals. Comparison with relaxation times for carboxy-substituted triarylmethyl radicals shows that T1 exhibits little dependence on protonation or the nature of the substituent, which makes it useful for measuring O2 concentration, independent of pH. Insensitivity of T1 to changes in substituents is consistent with the assignment of the dominant contribution to spin lattice relaxation as a local mode that involves primarily atoms in the carbon and sulfur core. Values of T2 vary substantially with pH and the nature of the aryl group substituent, reflecting a range of dynamic processes. The narrow spectral widths for the amino-substituted triarylmethyl radicals facilitate spectral-spatial rapid scan electron paramagnetic resonance imaging, which was demonstrated with a phantom. The dependence of hyperfine splittings patterns on pH is revealed in spectral slices through the image.

  3. A triarylmethyl spin label for long-range distance measurement at physiological temperatures using T1 relaxation enhancement

    NASA Astrophysics Data System (ADS)

    Yang, Zhongyu; Bridges, Michael D.; López, Carlos J.; Rogozhnikova, Olga Yu.; Trukhin, Dmitry V.; Brooks, Evan K.; Tormyshev, Victor; Halpern, Howard J.; Hubbell, Wayne L.

    2016-08-01

    Site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) spectroscopy has become an important tool for measuring distances in proteins on the order of a few nm. For this purpose pairs of spin labels, most commonly nitroxides, are site-selectively introduced into the protein. Recent efforts to develop new spin labels are focused on tailoring the intrinsic properties of the label to either extend the upper limit of measurable distances at physiological temperature, or to provide a unique spectral lineshape so that selective pairwise distances can be measured in a protein or complex containing multiple spin label species. Triarylmethyl (TAM) radicals are the foundation for a new class of spin labels that promise to provide both capabilities. Here we report a new methanethiosulfonate derivative of a TAM radical that reacts rapidly and selectively with an engineered cysteine residue to generate a TAM containing side chain (TAM1) in high yield. With a TAM1 residue and Cu2+ bound to an engineered Cu2+ binding site, enhanced T1 relaxation of TAM should enable measurement of interspin distances up to 50 Å at physiological temperature. To achieve favorable TAM1-labeled protein concentrations without aggregation, proteins are tethered to a solid support either site-selectively using an unnatural amino acid or via native lysine residues. The methodology is general and readily extendable to complex systems, including membrane proteins.

  4. Temperature dependence of the electron spin-lattice relaxation rate from pulsed EPR of CUA and heme a in cytochrome c oxidase.

    PubMed Central

    Scholes, C P; Janakiraman, R; Taylor, H; King, T E

    1984-01-01

    This work shows the feasibility of using pulsed, saturation recovery EPR to study directly the magnetic relaxation properties of metal centers in cytochrome c oxidase in the 1.5-20 K range. Heme a and CuA both showed remarkably similar Tn temperature dependences in their spin-lattice relaxation rates. Either both are in environments with very similar protein backbone configurations (Stapleton, H.J., J.P. Allen, C.P. Flynn, D.G. Stinson, and S.R. Kurtz, 1980, Phys. Rev. Lett., 45:1456-1459; Allen, J.P., J.T. Colvin, D.G. Stinson, C.P. Flynn, and H.J. Stapleton, 1982, Biophys. J., 38:299-310), or the CuA is relaxed by nearby heme a. Spin-lattice relaxation of the nitrosylferrocytochrome a3 center in mixed valence oxidase showed enhancement of relaxation by a nearby paramagnetic center, most likely heme a. PMID:6329343

  5. Dyakonov-perel electron spin relaxation in a highly degenerate wurtzite semiconductor

    NASA Astrophysics Data System (ADS)

    Rudolph, J.; Buß, J. H.; Semond, F.; Hägele, D.

    2013-12-01

    The doping density dependence of the electron spin lifetime in n-type bulk GaN is investigated up to the highly degenerate regime by time-resolved Kerr-rotation spectroscopy. We find a non-monotonic doping density dependence with maximum spin lifetimes at the onset of degeneracy. The reduction of spin lifetimes in the degenerate regime shows a weak τs∝nD-2/3 density dependence, in full agreement with Dyakonov-Perel theory.

  6. Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source.

    PubMed

    Lord, J S; McKenzie, I; Baker, P J; Blundell, S J; Cottrell, S P; Giblin, S R; Good, J; Hillier, A D; Holsman, B H; King, P J C; Lancaster, T; Mitchell, R; Nightingale, J B; Owczarkowski, M; Poli, S; Pratt, F L; Rhodes, N J; Scheuermann, R; Salman, Z

    2011-07-01

    The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.

  7. Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source

    SciTech Connect

    Lord, J. S.; McKenzie, I.; Baker, P. J.; Cottrell, S. P.; Giblin, S. R.; Hillier, A. D.; Holsman, B. H.; King, P. J. C.; Nightingale, J. B.; Pratt, F. L.; Rhodes, N. J.; Blundell, S. J.; Lancaster, T.; Good, J.; Mitchell, R.; Owczarkowski, M.; Poli, S.; Scheuermann, R.; Salman, Z.

    2011-07-15

    The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.

  8. Spin relaxation in graphene nanoribbons in the presence of substrate surface roughness

    NASA Astrophysics Data System (ADS)

    Chaghazardi, Zahra; Touski, Shoeib Babaee; Pourfath, Mahdi; Faez, Rahim

    2016-08-01

    In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin flipping rate and therefore reduction of the spin-polarization, whereas a longer correlation length makes AGNR surface smoother and increases spin-polarization. Moreover, spin diffusion length of carriers is extracted and its dependency on the roughness parameters is investigated. In agreement with experimental data, the spin diffusion length for various substrate ranges between 2 and 340 μm. Our results indicate the importance of surface roughness on spin-transport in graphene.

  9. Nuclear spin-lattice relaxation at field-induced level crossings in a Cr8F8 pivalate single crystal

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shoji

    2016-01-01

    We construct a microscopic theory for the proton spin-lattice relaxation-rate 1 / T1 measurements around field-induced level crossings in a single crystal of the trivalent chromium ion wheel complex [Cr8F8(OOCtBu)16] at sufficiently low temperatures [E. Micotti et al., Phys. Rev. B 72 (2005) 020405(R)]. Exactly diagonalizing a well-equipped spin Hamiltonian for the individual clusters and giving further consideration to their possible interactions, we reveal the mechanism of 1 / T1 being single-peaked normally at the first level crossing but double-peaked intriguingly around the second level crossing. We wipe out the doubt about poor crystallization and find out a solution-intramolecular alternating Dzyaloshinsky-Moriya interaction combined with intermolecular coupling of antiferromagnetic character, each of which is so weak as several tens of mK in magnitude.

  10. Study of the Ground State Properties of LiHoxY1-xF4 Using Muon Spin Relaxation

    SciTech Connect

    Rodriguez, Jose A.; Aczel, Adam A.; Carlo, Jeremy; Dunsiger, Sarah; Macdougall, Gregory J; Russo, Peter L.; Savici, Andrei T; Uemura, Yasutomo J.; Wiebe, Christopher; Luke, Graeme M.

    2010-09-01

    LiHoxY1-xF4 is an insulator where the magnetic Ho3+ ions have an Ising character and interact mainly through magnetic dipolar fields. We used the muon spin relaxation technique to study the nature of its ground state for samples with x 0.25. In contrast with some previous works, we did not find canonical spin glass behavior down to 15 mK. Instead, below 300 mK we observed temperature-independent dynamic magnetism characterized by a single correlation time. The 300 mK energy scale corresponds to the Ho3+ hyperfine interaction strength, suggesting that this interaction may be involved in the dynamic behavior of the system.

  11. The spatial effect of protein deuteration on nitroxide spin-label relaxation: Implications for EPR distance measurement

    NASA Astrophysics Data System (ADS)

    El Mkami, Hassane; Ward, Richard; Bowman, Andrew; Owen-Hughes, Tom; Norman, David G.

    2014-11-01

    Pulsed electron-electron double resonance (PELDOR) coupled with site-directed spin labeling is a powerful technique for the elucidation of protein or nucleic acid, macromolecular structure and interactions. The intrinsic high sensitivity of electron paramagnetic resonance enables measurement on small quantities of bio-macromolecules, however short relaxation times impose a limit on the sensitivity and size of distances that can be measured using this technique. The persistence of the electron spin-echo, in the PELDOR experiment, is one of the most crucial limitations to distance measurement. At a temperature of around 50 K one of the predominant factors affecting persistence of an echo, and as such, the sensitivity and measurable distance between spin labels, is the electron spin echo dephasing time (Tm). It has become normal practice to use deuterated solvents to extend Tm and recently it has been demonstrated that deuteration of the underlying protein significantly extends Tm. Here we examine the spatial effect of segmental deuteration of the underlying protein, and also explore the concentration and temperature dependence of highly deuterated systems.

  12. Muon spin relaxation and rotation studies of the filled skutterudite alloys praseodymium osmium ruthenium antimonide and praseodymium lanthanum osmium antimonide

    NASA Astrophysics Data System (ADS)

    Shu, Lei

    Some filled skutterudite compounds have recently been found to exhibit very interesting properties. The first Pr-based heavy-fermion superconductor, PrOs4Sb12, is an intriguing material due to the unusual properties of both its normal and superconducting states. Comprehensive muon spin rotation and relaxation studies and magnetic susceptibility measurements, described in this dissertation, have been performed to investigate the microscopic properties of PrOs4Sb12 and its Ru and La doped alloys. The temperature dependence of penetration depth measured in the vortex state of PrOs4Sb12 using transverse-field muon spin rotation (TF-muSR) is weaker than those measured by radiofrequency measurements. A scenario based on two-band superconductivity in PrOs4Sb 12, is proposed to resolve this difference. TF-muSR experiments also suggest the suppression of superfluid density with Ru doping, probably due to impurity scattering. In addition, magnetic susceptibility data as well as analysis of the muSR data in PrOs4Sb12 reveal a nearly linear relation of mu+ Knight shift vs. magnetic susceptibility. This suggests that the muon charge does not affect the crystalline electric field splitting of Pr3+ near neighbors. Additional evidence comes from the fact that the superconducting transition temperature Tc measured from muSR is consistent with the bulk superconducting values. Zero-field muon spin relaxation (ZF-muSR) experiments have been carried out in the Pr(Os1-xRux) 4Sb12 and Pr1-yLayOs 4Sb12 alloy systems to investigate the time-reversal symmetry (TRS) breaking found in an earlier ZF-muSR study of the end compound PrOs 4Sb12. The results from measurements at KEK, Japan, suggest that Ru doping is considerably more efficient than La doping in suppressing TRS breaking superconducting in PrOs4Sb12. However, we think that the spontaneous local field that indicates TRS breaking detected by ZF-muSR may depend on sample quality if those fields are from inhomogeneity in the

  13. Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory

    NASA Astrophysics Data System (ADS)

    Zimmermann, Bernd; Mavropoulos, Phivos; Long, Nguyen H.; Gerhorst, Christian-Roman; Blügel, Stefan; Mokrousov, Yuriy

    2016-04-01

    The Fermi surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several elemental metals are studied by ab initio calculations. We focus first on the anisotropy of the EYP as a function of the direction of the spin-quantization axis [B. Zimmermann et al., Phys. Rev. Lett. 109, 236603 (2012), 10.1103/PhysRevLett.109.236603]. We analyze in detail the origin of the gigantic anisotropy in 5 d hcp metals as compared to 5 d cubic metals by band structure calculations and discuss the stability of our results against an applied magnetic field. We further present calculations of light (4 d and 3 d ) hcp crystals, where we find a huge increase of the EYP anisotropy, reaching colossal values as large as 6000 % in hcp Ti. We attribute these findings to the reduced strength of spin-orbit coupling, which promotes the anisotropic spin-flip hot loops at the Fermi surface. In order to conduct these investigations, we developed an adapted tetrahedron-based method for the precise calculation of Fermi surfaces of complicated shape and accurate Fermi-surface integrals within the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

  14. Nitroxide spin labels as EPR reporters of the relaxation and magnetic properties of the heme-copper site in cytochrome bo3, E. coli.

    PubMed

    Oganesyan, Vasily S; White, Gaye F; Field, Sarah; Marritt, Sophie; Gennis, Robert B; Yap, Lai Lai; Thomson, Andrew J

    2010-11-01

    A nitroxide spin label (SL) has been used to probe the electron spin relaxation times and the magnetic states of the oxygen-binding heme-copper dinuclear site in Escherichia coli cytochrome bo(3), a quinol oxidase (QO), in different oxidation states. The spin lattice relaxation times, T(1), of the SL are enhanced by the paramagnetic metal sites in QO and hence show a strong dependence on the oxidation state of the latter. A new, general form of equations and a computer simulation program have been developed for the calculation of relaxation enhancement by an arbitrary fast relaxing spin system of S ≥ 1/2. This has allowed us to obtain an accurate estimate of the transverse relaxation time, T (2), of the dinuclear coupled pair Fe(III)-Cu(B)(II) in the oxidized form of QO that is too short to measure directly. In the case of the F' state, the relaxation properties of the heme-copper center have been shown to be consistent with a ferryl [Fe(IV)=O] heme and Cu(B)(II) coupled by approximately 1.5-3 cm(-1) to a radical. The magnitude suggests that the coupling arises from a radical form of the covalently linked tyrosine-histidine ligand to Cu(II) with unpaired spin density primarily on the tyrosine component. This work demonstrates that nitroxide SLs are potentially valuable tools to probe both the relaxation and the magnetic properties of multinuclear high-spin paramagnetic active sites in proteins that are otherwise not accessible from direct EPR measurements.

  15. Mechanism of Relaxation Enhancement of Spin Labels in Membranes by Paramagnetic Ion Salts: Dependence on 3 d and 4 f Ions and on the Anions

    NASA Astrophysics Data System (ADS)

    Livshits, V. A.; Dzikovski, B. G.; Marsh, D.

    2001-02-01

    Progressive saturation EPR measurements and EPR linewidth determinations have been performed on spin-labeled lipids in fluid phospholipid bilayer membranes to elucidate the mechanisms of relaxation enhancement by different paramagnetic ion salts. Such paramagnetic relaxation agents are widely used for structural EPR studies in biological systems, particularly with membranes. Metal ions of the 3d and 4f series were used as their chloride, sulfate, and perchlorate salts. For a given anion, the efficiency of relaxation enhancement is in the order Mn2+ ≥ Cu2+ > Ni2+ > Co2+ ≈ Dy3+. A pronounced dependence of the paramagnetic relaxation enhancement on the anion is found in the order ClO-4 > Cl- > SO2-4. This is in the order of the octanol partition coefficients multiplied by spin exchange rate constants that were determined for the different paramagnetic salts in methanol. Detailed studies coupled with theoretical estimates reveal that, for the chlorides and perchlorates of Ni2+ (and Co2+), the relaxation enhancements are dominated by Heisenberg spin exchange interactions with paramagnetic ions dissolved in fluid membranes. The dependence on membrane composition of the relaxation enhancement by intramembrane Heisenberg exchange indicates that the diffusion of the ions within the membrane takes place via water-filled defects. For the corresponding Cu2+ salts, additional relaxation enhancements arise from dipolar interactions with ions within the membrane. For the case of Mn2+ salts, static dipolar interactions with paramagnetic ions in the aqueous phase also make a further appreciable contribution to the spin-label relaxation enhancement. On this basis, different paramagnetic agents may be chosen to optimize sensitivity to different structurally correlated interactions. These results therefore will aid further spin-label EPR studies in structural biology.

  16. On the measurement of 15N-{ 1H} nuclear Overhauser effects. 2. Effects of the saturation scheme and water signal suppression

    NASA Astrophysics Data System (ADS)

    Ferrage, Fabien; Reichel, Amy; Battacharya, Shibani; Cowburn, David; Ghose, Ranajeet

    2010-12-01

    Measurement of steady-state 15N-{ 1H} nuclear Overhauser effects forms a cornerstone of most methods to determine protein backbone dynamics from spin-relaxation data, since it is the most reliable probe of very fast motions on the ps-ns timescale. We have, in two previous publications (J. Magn. Reson. 192 (2008) 302-313; J. Am. Chem. Soc. 131 (2009) 6048-6049) reevaluated spin-dynamics during steady-state (or "saturated") and reference experiments, both of which are required to determine the NOE ratio. Here we assess the performance of several windowed and windowless sequences to achieve effective saturation of protons in steady-state experiments. We also evaluate the influence of the residual water signal due to radiation damping on the NOE ratio. We suggest a recipe that allows one to determine steady-state 15N-{ 1H} NOE's without artifacts and with the highest possible accuracy.

  17. 7Li Spin-Lattice Relaxation at Low Temperatures in a Superionic Conductor β-LiGa

    NASA Astrophysics Data System (ADS)

    Endou, Shigeki; Ohno, Takashi; Kishimoto, Yutaka; Nishioka, Daisuke; Michihiro, Yoshitaka; Kawasaki, Yu; Ideta, Yukiichi; Kuriyama, Kazuo; Hamanaka, Hiromi; Yahagi, Masahito

    2009-10-01

    In order to investigate the Li+ ionic diffusion and the electronic states in a mixed conductor β-LiGa with high Li+ ionic diffusibility and electron/hole conductivity, 7Li NMR linewidth and spin-lattice relaxation measurements have been performed in 44.0, 47.0, and 50.0 at. % Li β-LiGa samples at 10.03 MHz in the temperature range between 10 and 320 K. The onset temperature TMN=70 K of the motional narrowing in 50.0 at. % sample has been determined from the temperature dependence of the linewidth. The Li+ ionic diffusion is found to contribute to the spin-lattice relaxation rate 1/T1 down to ˜0.5 TMN even below TMN where the motional narrowing does not occur. The high diffusibility of Li+ ions has been proved from a microscopic point of view. At low temperatures, the relations 1/T1T=3.5× 10-4, 3.8× 10-4, and 5.1× 10-4 s-1 K-1 are observed in 44.0, 47.0, and 50.0 at. % Li samples, respectively. The density of states of conduction electrons at the Fermi level in these compounds becomes higher with increasing Li content, which is consistent with the predictions by band calculations.

  18. Muon spin relaxation studies on magnetic properties of organic conductors Pd(dmit)2 salts and α-(BETS)2I3

    NASA Astrophysics Data System (ADS)

    Ohira-Kawamura, S.; Tamura, M.; Kato, R.; Hiraki, K.; Takahashi, T.; Iwasaki, M.

    2010-04-01

    Magnetic properties of organic conductors β'-Et2Me2Sb[Pd(dmit)2]2 (Et = C2H5, Me = CH3), P21/m crystal of EtMe3P[Pd(dmit)2]2 and α-(BETS)2I3 were investigated by muon spin relaxation (μSR) method. It has been suggested that Et2Me2Sb[Pd(dmit)2]2 exhibits a charge separation phase below ~70 K and that EtMe3P[Pd(dmit)2]2 exhibits a spin-Peierls-like state below ~25 K although it has a quasi two-dimensional structure. Our zero-field μSR results indicate that these Pd(dmit)2 salts show quite similar behavior to an organic spin-Peierls system although changes in the μSR time spectra of the EtMe3P salt was ambiguous. For α-(BETS)2I3, a metal-insulator transition is expected to occur at TMI ~ 50 K. We observed a slight enhancement of the muon spin relaxation below TMI and it gradually became remarkable at lower temperatures. The present result may reveal the existence of a spin-singlet ground state showing similar temperature dependence of the muon spin relaxation rate to that in the Pd(dmit)2 salts. However, the possibility that the relaxation in this system originates from magnetic fluctuations is also still conceivable.

  19. Relaxation-based distance measurements between a nitroxide and a lanthanide spin label

    NASA Astrophysics Data System (ADS)

    Jäger, H.; Koch, A.; Maus, V.; Spiess, H. W.; Jeschke, G.

    2008-10-01

    Distance measurements by electron paramagnetic resonance techniques between labels attached to biomacromolecules provide structural information on systems that cannot be crystallized or are too large to be characterized by NMR methods. However, existing techniques are limited in their distance range and sensitivity. It is anticipated by theoretical considerations that these limits could be extended by measuring the enhancement of longitudinal relaxation of a nitroxide label due to a lanthanide complex label at cryogenic temperatures. The relaxivity of the dysprosium complex with the macrocyclic ligand DOTA can be determined without direct measurements of longitudinal relaxation rates of the lanthanide and without recourse to model compounds with well defined distance by analyzing the dependence of relaxation enhancement on either temperature or concentration in homogeneous glassy frozen solutions. Relaxivities determined by the two calibration techniques are in satisfying agreement with each other. Error sources for both techniques are examined. A distance of about 2.7 nm is measured in a model compound of the type nitroxide-spacer-lanthanide complex and is found in good agreement with the distance in a modeled structure. Theoretical considerations suggest that an increase of the upper distance limit requires measurements at lower fields and temperatures.

  20. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    DOE PAGES

    S. -H. Baek; Gu, G. D.; Utz, Y.; Hucker, M.; Buchner, B.; Grafe, H. -J.

    2015-10-26

    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for largemore » fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

  1. 15N chemical shift tensors and conformation of solid polypeptides containing 15N-labeled glycine residue by 15N NMR

    NASA Astrophysics Data System (ADS)

    Shoji, Akira; Ozaki, Takuo; Fujito, Teruaki; Deguchi, Kenzo; Ando, Isao; Magoshi, Jun

    1998-01-01

    The correlation between the isotropic 15N chemical shift ( δiso) and 15N chemical shift tensor components ( δ11, δ22 and δ33) and the main-chain conformation such as the polyglycine I (PGI: β-sheet), II (PGII: 3 1-helix), α-helix and β-sheet forms of solid polypeptides [Gly∗,X] n consisting of 15N-labeled glycine (Gly∗) and other amino acids (X: natural abundance of 15N) has been studied by solid-state 15N NMR method. A series of polypeptides [Gly∗,X] n (X = glycine, L-alanine, L-leucine, L-valine, L-isoleucine, β-benzyl L-aspartate, γ-benzyl L-glutamate, ɛ-carbobenzoxy L-lysine, and sarcosine) were synthesized by the α-amino acid N-carboxy anhydride (NCA) method. Conformations of these polypeptides in the solid state were characterized on the basis of conformation-dependent 13C chemical shifts in the 13C cross-polarization-magic angle spinning (CP-MAS) NMR spectra and by the characteristic bands in the IR and far-IR spectra. The δiso, δ11, δ22 and δ33 of the polypetides were determined from the 15N CP-MAS and 15N CP-static (powder pattern) spectra. It was found that the δiso, δ11, δ22 and δ33 in the PGI form (δ 83.5, 185, 40.7 and 25 ppm, resp.) are upfield from those in the PGII form (88.5, 194, 42.1 and 29 ppm, resp.), which were reproduced by the calculated 15N shielding constants using the finite perturbation theory (FPT)-INDO method. It was also found that the δ22 of the Gly∗ of [Gly∗,X] n is closely related to the main-chain conformation and the neighboring amino acid sequence, although the δiso is almost independent of the glycine content and conformation. Consequently, the δ22 value of Gly∗ containing copolypeptides is useful for the structural (main-chain conformation and neighboring amino acid sequence) analysis in the solid state by 15N NMR, if the 15N-labeled copolypeptide or natural protein can be provided. In addition, it is shown that the δiso of the glycine residue is useful for the conformational study of some

  2. Relaxation after quantum quenches in the spin-1/2 Heisenberg XXZ chain

    NASA Astrophysics Data System (ADS)

    Fagotti, Maurizio; Collura, Mario; Essler, Fabian H. L.; Calabrese, Pasquale

    2014-03-01

    We consider the time evolution after quantum quenches in the spin-1/2 Heisenberg XXZ quantum spin chain with Ising-type anisotropy. The time evolution of short-distance spin-spin correlation functions is studied by numerical tensor network techniques for a variety of initial states, including Néel and Majumdar-Ghosh states and the ground state of the XXZ chain at large values of the anisotropy. The various correlators appear to approach stationary values, which are found to be in good agreement with the results of exact calculations of stationary expectation values in appropriate generalized Gibbs ensembles. In particular, our analysis shows how symmetries of the post-quench Hamiltonian that are broken by particular initial states are restored at late times.

  3. Impact of artificial lateral quantum confinement on exciton-spin relaxation in a two-dimensional GaAs electronic system

    SciTech Connect

    Kiba, Takayuki Murayama, Akihiro; Tanaka, Toru; Tamura, Yosuke; Higo, Akio; Thomas, Cedric; Samukawa, Seiji

    2014-10-15

    We demonstrate the effect of artificial lateral quantum confinement on exciton-spin relaxation in a GaAs electronic system. GaAs nanodisks (NDs) were fabricated from a quantum well (QW) by top-down nanotechnology using neutral-beam etching aided by protein-engineered bio-nano-templates. The exciton-spin relaxation time was 1.4 ns due to ND formation, significantly extended compared to 0.44 ns for the original QW, which is attributed to weakening of the hole-state mixing in addition to freezing of the carrier momentum. The temperature dependence of the spin-relaxation time depends on the ND thickness, reflecting the degree of quantum confinement.

  4. Calculation of the electron spin relaxation times in InSb and InAs by the projection-reduction method

    SciTech Connect

    Kang, Nam Lyong

    2014-12-07

    The electron spin relaxation times in a system of electrons interacting with piezoelectric phonons mediated through spin-orbit interactions were calculated using the formula derived from the projection-reduction method. The results showed that the temperature and magnetic field dependence of the relaxation times in InSb and InAs were similar. The piezoelectric material constants obtained by a comparison with the reported experimental result were P{sub pe}=4.0×10{sup 22} eV/m for InSb and P{sub pe}=1.2×10{sup 23} eV/m for InAs. The result also showed that the relaxation of the electron spin by the Elliot-Yafet process is more relevant for InSb than InAs at a low density.

  5. Nuclear spin relaxation times in hydrogen-helium and methane-helium slush at 4 MHz using pulsed NMR

    NASA Astrophysics Data System (ADS)

    Hamida, J. A.

    2005-03-01

    We compare the nuclear spin-lattice and nuclear spin-spin relaxation times observed for small grains of hydrogen suspended in liquid helium (hydrogen-helium ``slush'') with that of methane-helium ``slush.'' The transport properties of these ``slush'' materials are critical to NASA's goal of realizing atomic propellant designs for future spacecraft. Atoms of active propellants are stored cryogenically in a host matrix such as hydrogen (H2) or methane (CH4) to prevent recombination while liquid helium is ideal for holding the host matrix and for easy transportation. The host matrix must therefore be stable in liquid helium. We find that for hydrogen ``slush,'' NMR rate is consistent with scattering at grain boundaries due to the large electric quadrupole moment of hydrogen; on the other hand the ``slush'' rate for methane is consistent with internal diffusion as opposed to surface scattering. We conclude that for atomic propellants, methane is a better host than hydrogen because grains of methane are better isolated from the helium bath.

  6. Measured Electron Spin Relaxation Rates in Frozen Solutions of Azurin, VITAMIN-B12R, and Nitrosyl Ferrous Myoglobin.

    NASA Astrophysics Data System (ADS)

    Muench, Philip James

    Rates in frozen glycerin/water solutions at temperatures between 1.4 K and 20 K are reported for a copper-containing protein, azurin, and a cobalt-containing biomolecular complex, vitamin B_{rm 12r}, the paramagnetic product of the photolysis of coenzyme B_{12}. Results are interpreted in terms of a spectral dimensionality. Rates are also reported for nitrosyl ferrous myoglobin in frozen water solution, which exhibits a dominant one-phonon relaxation process up to 20 K and thus does not reveal spectral dimensionality. The anomalous variation of rate with temperature observed in several iron-containing proteins is not conspicuous here. In a model two-phonon mechanism of relaxation, temperature dependence is fixed by a spectral dimensionality, m, which specifies the variation of vibrational density of states with frequency rho(nu ) ~ nu ^{rm m-1} and is named in analogy with the Debye density of states in 1-, 2-, and 3-dimensional crystals. At sufficiently high temperatures, a non-resonant two-phonon process (Raman) should dominate the relaxation of a paramagnetic ion unless low-lying (under ^{~}70 cm^ {-1}) electronic states are present, as in many rare earths and in high spin ferric complexes, including many ferric proteins. The temperature dependence of the Raman rate for a Kramers ion (odd number of electrons) is T^{rm 3+2m} if temperature is sufficiently lower than Theta = hnu_{rm max} /k, the Debye temperature. The values of m from relaxation data on frozen solutions of a protein have sometimes been dependent upon solvent conditions. The maximum values of m for heme proteins, iron-sulfur proteins, and one copper -and-iron-containing protein, have ranged from about 1.3 to 1.8. Pulse saturation/recovery was used. The recoveries were not exponential, but rates were estimated from semilogarithmic displays of signals or from numerical fitting. The temperature dependence of the rates for azurin between 1.5 K and 22 K can be fit with a spectral dimensionality of 3 and

  7. EPR Line Shifts and Line Shape Changes Due to Heisenberg Spin Exchange and Dipole–Dipole Interactions of Nitroxide Free Radicals in Liquids: 9. An Alternative Method to Separate the Effects of the Two Interactions Employing 15N and 14N

    PubMed Central

    2015-01-01

    A method to separate the effects of Heisenberg spin exchange (HSE) and dipole–dipole (DD) interactions on EPR spectra of nitroxide spin probes in solution by employing 15N and 14N nitroxide spin probes in parallel experiments is developed theoretically and tested experimentally. Comprehensive EPR measurements are reported of 4-oxo-2,2,6,6-tetramethylpiperidine-d16;1-15N-1-oxyl (perdeuterated 15N Tempone; 15pDT), in 70 wt % aqueous glycerol as functions of concentration and temperature. The method, termed the relative broadening constant method (RBCM), is demonstrated by using the present results together with those in the literature that employed perdeuterated 14N Tempone (14pDT) under identical conditions. In principle, the separation of DD and HSE is dependent on the model of diffusion and molecular-kinetic parameters; however, within present day experimental uncertainties, the RBCM method turns out to be insensitive to the model. The earlier methods to separate DD and HSE by measuring the dispersion component introduced by the two interactions shows general agreement with the RBCM; however, there are discrepancies larger than estimated uncertainties due to random errors. Thus, further support is found for Salikhov’s recent theory of the effects of DD and HSE on EPR spectra (Appl. Magn. Reson.2010, 38, 237); however, detailed confirmation is still lacking. The RBCM affords a possible approach to separate HSE and DD in spectra complicated by slow motion and/or overlap with other resonance lines, allowing the method to be used in situations more complicated than low-viscosity simple liquids. PMID:25035905

  8. EPR and spin-lattice relaxation of rare-earth activated centres in Y 2SiO 5 single crystals

    NASA Astrophysics Data System (ADS)

    Kurkin, I. N.; Chernov, K. P.

    1980-08-01

    An investigation of the EPR spectra and spin-lattice relaxation of Ce 3+, Nd 3+ and Yb 3+ ions in Y 2SiO 5 single crystals has been carried out. Two different EPR spectra for each rare-earth ion are observed due to a substitution of Y 1 and Y 2 sites crytals. Spin-lattice relaxation times for both activated centres are shown to be essentially different, although static crystal field of Y 1 and Y 2 sites differ slightly.

  9. Ligand protons in a frozen solution of copper histidine relax via a T1e-driven three-spin mechanism

    NASA Astrophysics Data System (ADS)

    Stoll, S.; Epel, B.; Vega, S.; Goldfarb, D.

    2007-10-01

    Davies electron-nuclear double resonance spectra can exhibit strong asymmetries for long mixing times, short repetition times, and large thermal polarizations. These asymmetries can be used to determine nuclear relaxation rates in paramagnetic systems. Measurements of frozen solutions of copper(L-histidine)2 reveal a strong field dependence of the relaxation rates of the protons in the histidine ligand, increasing from low (g‖) to high (g⊥) field. It is shown that this can be attributed to a concentration-dependent T1e-driven relaxation process involving strongly mixed states of three spins: the histidine proton, the Cu(II) electron spin of the same complex, and another distant electron spin with a resonance frequency differing from the spectrometer frequency approximately by the proton Larmor frequency. The protons relax more efficiently in the g⊥ region, since the number of distant electrons able to participate in this relaxation mechanism is higher than in the g‖ region. Analytical expressions for the associated nuclear polarization decay rate Teen-1 are developed and Monte Carlo simulations are carried out, reproducing both the field and the concentration dependences of the nuclear relaxation.

  10. A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin-lattice relaxation data for the methyl groups in solids.

    PubMed

    Bernatowicz, Piotr; Shkurenko, Aleksander; Osior, Agnieszka; Kamieński, Bohdan; Szymański, Sławomir

    2015-11-21

    The theory of nuclear spin-lattice relaxation in methyl groups in solids has been a recurring problem in nuclear magnetic resonance (NMR) spectroscopy. The current view is that, except for extreme cases of low torsional barriers where special quantum effects are at stake, the relaxation behaviour of the nuclear spins in methyl groups is controlled by thermally activated classical jumps of the methyl group between its three orientations. The temperature effects on the relaxation rates can be modelled by Arrhenius behaviour of the correlation time of the jump process. The entire variety of relaxation effects in protonated methyl groups have recently been given a consistent quantum mechanical explanation not invoking the jump model regardless of the temperature range. It exploits the damped quantum rotation (DQR) theory originally developed to describe NMR line shape effects for hindered methyl groups. In the DQR model, the incoherent dynamics of the methyl group include two quantum rate (i.e., coherence-damping) processes. For proton relaxation only one of these processes is relevant. In this paper, temperature-dependent proton spin-lattice relaxation data for the methyl groups in polycrystalline methyltriphenyl silane and methyltriphenyl germanium, both deuterated in aromatic positions, are reported and interpreted in terms of the DQR model. A comparison with the conventional approach exploiting the phenomenological Arrhenius equation is made. The present observations provide further indications that incoherent motions of molecular moieties in the condensed phase can retain quantum character over much broader temperature range than is commonly thought. PMID:26451661

  11. Electron Spin-Lattice Relaxation in Two Heme Iron and Two Blue-Copper Proteins at Liquid Helium Temperatures

    NASA Astrophysics Data System (ADS)

    Thayer, Bradley Denton

    1990-01-01

    The relaxation rates in frozen aqueous solutions of whale ferri-myoglobin azide, bovine ferri-hemoglobin azide, cupric azurin (P. aeruginosa) and cupric spinach plastocyanin were measured at 9.5 GHz using the pulse-saturation recovery method. Measurements covered a temperature range of 1.4 K to as high as 22 K, with corresponding relaxation rates up to 10^5/sec. Improvements in the equipment and the methods of analysis have enabled more stringent tests of the temperature dependence of the rates. In particular, several models proposed in the literature to explain the anomalous temperature dependence of the Raman rates in proteins are shown to be insufficient, including two fractal models. In addition, it is shown that any model based exclusively on the protein structure fails due to the diversity of the data under various solvent conditions. A general functional form consistent with a crossover in the vibrational properties is proposed instead, similar to the localization crossover in amorphous materials. The effect on the relaxation rate of several cosolvents and solutes is also examined. The effect on the direct process is much more pronounced than on the Raman region. The differences are shown to be consistent with changes in the velocity of sound at room temperature caused by the addition of cosolvents and solutes. Finally, the EPR recovery form is analyzed. We propose that the deviations in the recovery from an exponential form are due to a distribution of relaxation rates. The source of the distribution is most likely sample heating in the lower temperatures and a distribution of conformations frozen in near the paramagnetic site in the higher temperatures. It is not likely that it is caused by spin-spin interactions. The exact form of the distribution is unclear, but the most successful functional form for the recoveries is a stretched exponential with an exponent ranging from 0.5 to 1.0. However, a simple exponential fit to a limited portion of the recovery

  12. Investigation of a new model of dipolar-coupled nuclear spin relaxation and applications of dynamic nuclear polarization

    NASA Astrophysics Data System (ADS)

    Sorte, Eric G.

    This work presents the results of various investigations using various techniques of hyperpolarizing the nuclei of atoms. Hyperpolarization implies magnetic order in excess of the thermal order obtained naturally as described by Curie's law. The main portion of this work presents the results of a detailed experimental exploration of predictions arising from a new model of transverse nuclear spin relaxation in quantum systems, based on possible manifestations of microscopic chaos in quantum systems. Experiments have been carried out on a number of hyperpolarized xenon samples, each differing in its relative percentage of xenon isotopes in order to vary the homonuclear and heteronuclear dipole couplings in the spin system. The experiments were performed under a variety of conditions in an attempt to observe the behaviors predicted by the model. Additionally, much more extensive measurements were made on a number of samples of solid CaF2 in both single crystal and powder forms. These samples, although thermally polarized, were observed with superior signal to noise ratios than even the hyperpolarized xenon solids, allowing for more precise measurements for comparison to the theory. This work thus contains the first experimental evidence for the majority of the model's predictions. Additionally, this work contains the first precise measurements of the frequency-shift enhancement parameters for 129Xe and krypton in the presence of spin-polarized Rb. The determination of these important numbers will be useful to many groups who utilize spin-exchange optical pumping in their labs. This work built on the prior knowledge of a precise number for the frequency-shift enhancement parameter of 3He in Rb vapor. Finally, I detail work using NMR to detect nuclear-spin polarization enhancement in silicon phosphorus by a novel, photo-induced hyperpolarization technique developed by the Boehme research group at the University of Utah. Significant nuclear polarization enhancements were

  13. Measurement of solute proton spin-lattice relaxation times in water using the 1,3,3,1 sequence

    SciTech Connect

    Sankar, S.S.; Mole, P.A.; Coulson, R.L.

    1986-12-01

    /sup 1/H NMR spin-lattice relaxation times (T1) of the N-CH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D/sub 2/O and water using either the conventional inversion-recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP in equilibrium ATP + Cr) in aqueous solutions and perhaps in biological preparations.

  14. Off-resonance rotating frame spin-lattice NMR relaxation studies of phosphorus metabolite rotational diffusion in bovine lens homogenates

    SciTech Connect

    Caines, G.H.; Schleich, T.; Morgan, C.F. ); Farnsworth, P.N. )

    1990-08-21

    The rotational diffusion behavior of phosphorus metabolites present in calf lens cortical and nuclear homogenates was investigated by the NMR technique of {sup 31}P off-resonance rotating frame spin-lattice relaxation as a means of assessing the occurrence and extent of phosphorus metabolite-lens protein interactions. {sup 31}P NMR spectra of calf lens homogenates were obtained at 10 and 18{degree}C at 7.05 T. Effective rotational correlation times ({tau}{sub 0,eff}) for the major phosphorus metabolites present in cortical and nuclear bovine calf lens homogenates were derived from nonlinear least-squares analysis of R vs {omega}{sub e} data with the assumption of isotropic reorientational motion. Intramolecular dipole-dipole ({sup 1}H-{sup 31}P, {sup 31}P-{sup 31}P), chemical shift anisotropy (CSA), and solvent (water) translational intermolecular dipole-dipole ({sup 1}H-{sup 31}P) relaxation contributions were assumed in the analyses. A fast-exchange model between free and bound forms, was employed in the analysis of the metabolite R vs {omega}{sub e} curves to yield the fraction of free (unbound) metabolite ({Theta}{sub free}). The results of this study establish the occurrence of significant temperature-dependent (above and below the cold cataract phase transition temperature) binding of ATP (cortex) and PME (nucleus) and p{sub i} (nucleus) in calf lens.

  15. Diffusive behavior in LiMPO4 with M=Fe, Co, Ni probed by muon-spin relaxation

    NASA Astrophysics Data System (ADS)

    Sugiyama, Jun; Nozaki, Hiroshi; Harada, Masashi; Kamazawa, Kazuya; Ikedo, Yutaka; Miyake, Yasuhiro; Ofer, Oren; Månsson, Martin; Ansaldo, Eduardo J.; Chow, Kim H.; Kobayashi, Genki; Kanno, Ryoji

    2012-02-01

    In order to study the diffusive nature of lithium transition-metal phospho-olivines, we measured muon-spin relaxation (μ+SR) spectra for the polycrystalline LiMPO4 samples with M=Mn, Fe, Co, or Ni in the temperature range between 50 and 500 K. The μ+SR spectra under zero applied field are strongly affected by the magnetic moments of the 3d electrons in the M2+ ions so that, for LiMnPO4, it was difficult to detect the relaxation change caused by the diffusion due to the large Mn2+(S=5/2) moments. However, diffusive behavior was clearly observed via the relaxation due to nuclear dipolar fields above ˜150 K for LiFePO4, LiCoPO4, and LiNiPO4 as S decreased from 2 to 1. From the temperature dependence of the nuclear field fluctuation rate, self-diffusion coefficients of Li+ ions (DLi) at 300 K and its activation energy (Ea) were estimated, respectively, as ˜3.6(2)×10-10 cm2/s and Ea=0.10(2) eV for LiFePO4, ˜1.6(1)×10-10 cm2/s and Ea=0.10(1) eV for LiCoPO4, and ˜2.7(4)×10-10 cm2/s and Ea=0.17(2) eV for LiNiPO4, assuming that the diffusing Li+ ions jump between the regular site and interstitial sites.

  16. Neutron Spin-Echo Investigation of Slow Spin Dynamics in Kagome-Bilayer Frustrated Magnets as Evidence for Phonon Assisted Relaxation in SrCr{sub 9x}Ga{sub 12-9x}O{sub 19}

    SciTech Connect

    Mutka, H.; Ehlers, G.; Stewart, J. R.; Fouquet, P.; Payen, C.; Mevellec, J. Y.; Bono, D.; Mendels, P.; Blanchard, N.; Collin, G.

    2006-07-28

    A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagome bilayer compounds SrCr{sub 9x}Ga{sub 12-9x}O{sub 19} (x=0.95, SCGO) and Ba{sub 2}Sn{sub 2}ZnCr{sub 7x}Ga{sub 10-7x}O{sub 22} (x=0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at T{sub g}, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K ({approx_equal}T{sub g})relaxation rate activation energy E{sub a}=7{+-}0.4 meV, equal to the energy of a phonon mode, pointing out the role of spin-lattice coupling.

  17. Studies of a Large Odd-Numbered Odd-Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8 Mn.

    PubMed

    Baker, Michael L; Lancaster, Tom; Chiesa, Alessandro; Amoretti, Giuseppe; Baker, Peter J; Barker, Claire; Blundell, Stephen J; Carretta, Stefano; Collison, David; Güdel, Hans U; Guidi, Tatiana; McInnes, Eric J L; Möller, Johannes S; Mutka, Hannu; Ollivier, Jacques; Pratt, Francis L; Santini, Paolo; Tuna, Floriana; Tregenna-Piggott, Philip L W; Vitorica-Yrezabal, Iñigo J; Timco, Grigore A; Winpenny, Richard E P

    2016-01-26

    The spin dynamics of Cr8 Mn, a nine-membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8 Mn is a rare example of a large odd-membered AF ring, and has an odd-number of 3d-electrons present. Odd-membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated-spin ground states. The chemical synthesis and structures of two Cr8 Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground-spin-state crossing from S=1/2 to S=3/2 in Cr8 Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin-pair correlations and scalar-spin chirality, shows a non-collinear spin structure that fluctuates between non-planar states of opposite chiralities. PMID:26748964

  18. Studies of a Large Odd-Numbered Odd-Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8 Mn.

    PubMed

    Baker, Michael L; Lancaster, Tom; Chiesa, Alessandro; Amoretti, Giuseppe; Baker, Peter J; Barker, Claire; Blundell, Stephen J; Carretta, Stefano; Collison, David; Güdel, Hans U; Guidi, Tatiana; McInnes, Eric J L; Möller, Johannes S; Mutka, Hannu; Ollivier, Jacques; Pratt, Francis L; Santini, Paolo; Tuna, Floriana; Tregenna-Piggott, Philip L W; Vitorica-Yrezabal, Iñigo J; Timco, Grigore A; Winpenny, Richard E P

    2016-01-26

    The spin dynamics of Cr8 Mn, a nine-membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8 Mn is a rare example of a large odd-membered AF ring, and has an odd-number of 3d-electrons present. Odd-membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated-spin ground states. The chemical synthesis and structures of two Cr8 Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground-spin-state crossing from S=1/2 to S=3/2 in Cr8 Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin-pair correlations and scalar-spin chirality, shows a non-collinear spin structure that fluctuates between non-planar states of opposite chiralities.

  19. Fermi-level pinning, charge transfer, and relaxation of spin-momentum locking at metal contacts to topological insulators

    DOE PAGES

    Spataru, Catalin D.; Léonard, François

    2014-08-13

    Topological insulators are of interest for many applications in electronics and optoelectronics, but harnessing their unique properties requires detailed understanding and control of charge injection at electrical contacts. Here we present large-scale ab initio calculations of the electronic properties of Au, Ni, Pt, Pd, and graphene contacts to Bi2Se3. We show that regardless of the metal, the Fermi level is located in the conduction band, leading to n-type Ohmic contact to the first quintuplet. Furthermore, we find strong charge transfer and band-bending in the first few quintuplets, with no Schottky barrier for charge injection even when the topoplogical insulator ismore » undoped. Our calculations indicate that Au and graphene leave the spin-momentum locking mostly unaltered, but on the other hand, Ni, Pd, and Pt strongly hybridize with Bi2Se3 and relax spin-momentum locking. In conclusion, our results indicate that judicious choice of the contact metal is essential to reveal the unique surface features of topological insulators.« less

  20. Fermi-level pinning, charge transfer, and relaxation of spin-momentum locking at metal contacts to topological insulators

    SciTech Connect

    Spataru, Catalin D.; Léonard, François

    2014-08-13

    Topological insulators are of interest for many applications in electronics and optoelectronics, but harnessing their unique properties requires detailed understanding and control of charge injection at electrical contacts. Here we present large-scale ab initio calculations of the electronic properties of Au, Ni, Pt, Pd, and graphene contacts to Bi2Se3. We show that regardless of the metal, the Fermi level is located in the conduction band, leading to n-type Ohmic contact to the first quintuplet. Furthermore, we find strong charge transfer and band-bending in the first few quintuplets, with no Schottky barrier for charge injection even when the topoplogical insulator is undoped. Our calculations indicate that Au and graphene leave the spin-momentum locking mostly unaltered, but on the other hand, Ni, Pd, and Pt strongly hybridize with Bi2Se3 and relax spin-momentum locking. In conclusion, our results indicate that judicious choice of the contact metal is essential to reveal the unique surface features of topological insulators.

  1. Reexamination of relaxation of spins due to a magnetic field gradient: Identity of the Redfield and Torrey theories

    NASA Astrophysics Data System (ADS)

    Golub, R.; Rohm, Ryan M.; Swank, C. M.

    2011-02-01

    There is an extensive literature on magnetic-gradient-induced spin relaxation. Cates, Schaefer, and Happer, in a seminal publication, have solved the problem in the regime where diffusion theory (the Torrey equation) is applicable using an expansion of the density matrix in diffusion equation eigenfunctions and angular momentum tensors. McGregor has solved the problem in the same regime using a slightly more general formulation using the Redfield theory formulated in terms of the autocorrelation function of the fluctuating field seen by the spins and calculating the correlation functions using the diffusion-theory Green’s function. The results of both calculations were shown to agree for a special case. In the present work, we show that the eigenfunction expansion of the Torrey equation yields the expansion of the Green’s function for the diffusion equation, thus showing the identity of this approach with that of the Redfield theory. The general solution can also be obtained directly from the Torrey equation for the density matrix. Thus, the physical content of the Redfield and Torrey approaches are identical. We then introduce a more general expression for the position autocorrelation function of particles moving in a closed cell, extending the range of applicability of the theory.

  2. Magnetic field penetration depth of La(1.85)Sr(0.15)CuO4 measured by muon spin relaxation

    NASA Technical Reports Server (NTRS)

    Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Uemura, Y. J.

    1987-01-01

    Muon-spin-relaxation measurements have been performed on a high-Tc superconductor La(1.85)Sr(0.15)CuO4. In an external transverse magnetic field of 500 G, a magnetic field penetration depth of 2000 A at T = 10 K has been determined from the muon-spin-relaxation rate which increased with decreasing temperature below Tc. From this depth and the Pauli susceptibility, the superconducting carrier density is estimated at 3 x 10 to the 21st per cu cm. The zero-field relaxation rates above and below Tc were equal, which suggests that the superconducting state in this sample is not associated with detectable static magnetic ordering.

  3. Radical ions with nearly degenerate ground state: correlation between the rate of spin-lattice relaxation and the structure of adiabatic potential energy surface.

    PubMed

    Borovkov, V I; Beregovaya, I V; Shchegoleva, L N; Potashov, P A; Bagryansky, V A; Molin, Y N

    2012-09-14

    Paramagnetic spin-lattice relaxation (SLR) in radical cations (RCs) of the cycloalkane series in liquid solution was studied and analyzed from the point of view of the correlation between the relaxation rate and the structure of the adiabatic potential energy surface (PES) of the RCs. SLR rates in the RCs formed in x-ray irradiated n-hexane solutions of the cycloalkanes studied were measured with the method of time-resolved magnetic field effect in the recombination fluorescence of spin-correlated radical ion pairs. Temperature and, for some cycloalkanes, magnetic field dependences of the relaxation rate were determined. It was found that the conventional Redfield theory of the paramagnetic relaxation as applied to the results on cyclohexane RC, gave a value of about 0.2 ps for the correlation time of the perturbation together with an unrealistically high value of 0.1 T in field units for the matrix element of the relaxation transition. The PES structure was obtained with the DFT quantum-chemical calculations. It was found that for all of the cycloalkanes RCs considered, including low symmetric alkyl-substituted ones, the adiabatic PESes were surfaces of pseudorotation due to avoided crossing. In the RCs studied, a correlation between the SLR rate and the calculated barrier height to the pseudorotation was revealed. For RCs with a higher relaxation rate, the apparent activation energies for the SLR were similar to the calculated heights of the barrier. To rationalize the data obtained it was assumed that the vibronic states degeneracy, which is specific for Jahn-Teller active cyclohexane RC, was approximately kept in the RCs of substituted cycloalkanes for the vibronic states with the energies above and close to the barrier height to the pseudorotation. It was proposed that the effective spin-lattice relaxation in a radical with nearly degenerate low-lying vibronic states originated from stochastic crossings of the vibronic levels that occur due to fluctuations of

  4. Centric scan SPRITE for spin density imaging of short relaxation time porous materials.

    PubMed

    Chen, Quan; Halse, Meghan; Balcom, Bruce J

    2005-02-01

    The single-point ramped imaging with T1 enhancement (SPRITE) imaging technique has proven to be a very robust and flexible method for the study of a wide range of systems with short signal lifetimes. As a pure phase encoding technique, SPRITE is largely immune to image distortions generated by susceptibility variations, chemical shift and paramagnetic impurities. In addition, it avoids the line width restrictions on resolution common to time-based sampling, frequency encoding methods. The standard SPRITE technique is however a longitudinal steady-state imaging method; the image intensity is related to the longitudinal steady state, which not only decreases the signal-to-noise ratio, but also introduces many parameters into the image signal equation. A centric scan strategy for SPRITE removes the longitudinal steady state from the image intensity equation and increases the inherent image intensity. Two centric scan SPRITE methods, that is, Spiral-SPRITE and Conical-SPRITE, with fast acquisition and greatly reduced gradient duty cycle, are outlined. Multiple free induction decay (FID) points may be acquired during SPRITE sampling for signal averaging to increase signal-to-noise ratio or for T2* and spin density mapping without an increase in acquisition time. Experimental results show that most porous sedimentary rock and concrete samples have a single exponential T2* decay due to susceptibility difference-induced field distortion. Inhomogeneous broadening thus dominates, which suggests that spin density imaging can be easily obtained by SPRITE. PMID:15833624

  5. Centric scan SPRITE for spin density imaging of short relaxation time porous materials.

    PubMed

    Chen, Quan; Halse, Meghan; Balcom, Bruce J

    2005-02-01

    The single-point ramped imaging with T1 enhancement (SPRITE) imaging technique has proven to be a very robust and flexible method for the study of a wide range of systems with short signal lifetimes. As a pure phase encoding technique, SPRITE is largely immune to image distortions generated by susceptibility variations, chemical shift and paramagnetic impurities. In addition, it avoids the line width restrictions on resolution common to time-based sampling, frequency encoding methods. The standard SPRITE technique is however a longitudinal steady-state imaging method; the image intensity is related to the longitudinal steady state, which not only decreases the signal-to-noise ratio, but also introduces many parameters into the image signal equation. A centric scan strategy for SPRITE removes the longitudinal steady state from the image intensity equation and increases the inherent image intensity. Two centric scan SPRITE methods, that is, Spiral-SPRITE and Conical-SPRITE, with fast acquisition and greatly reduced gradient duty cycle, are outlined. Multiple free induction decay (FID) points may be acquired during SPRITE sampling for signal averaging to increase signal-to-noise ratio or for T2* and spin density mapping without an increase in acquisition time. Experimental results show that most porous sedimentary rock and concrete samples have a single exponential T2* decay due to susceptibility difference-induced field distortion. Inhomogeneous broadening thus dominates, which suggests that spin density imaging can be easily obtained by SPRITE.

  6. Measurement of multiple psi torsion angles in uniformly 13C,15N-labeled alpha-spectrin SH3 domain using 3D 15N-13C-13C-15N MAS dipolar-chemical shift correlation spectroscopy.

    PubMed

    Ladizhansky, Vladimir; Jaroniec, Christopher P; Diehl, Annette; Oschkinat, Hartmut; Griffin, Robert G

    2003-06-01

    We demonstrate the simultaneous measurement of several backbone torsion angles psi in the uniformly (13)C,(15)N-labeled alpha-Spectrin SH3 domain using two different 3D 15N-13C-13C-15N dipolar-chemical shift magic-angle spinning (MAS) NMR experiments. The first NCCN experiment utilizes double quantum (DQ) spectroscopy combined with the INADEQUATE type 13C-13C chemical shift correlation. The decay of the DQ coherences formed between 13C'(i) and 13C(alphai) spin pairs is determined by the "correlated" dipolar field due to 15N(i)-13C(alphai) and 13C'(i)-15N(i+1) dipolar couplings and is particularly sensitive to variations of the torsion angle in the regime |psi| > 140 degrees. However, the ability of this experiment to constrain multiple psi-torsion angles is limited by the resolution of the 13C(alpha)-(13)CO correlation spectrum. This problem is partially addressed in the second approach described here, which is an NCOCA NCCN experiment. In this case the resolution is enhanced by the superior spectral dispersion of the 15N resonances present in the 15N(i+1)-13C(alphai) part of the NCOCA chemical shift correlation spectrum. For the case of the 62-residue alpha-spectrin SH3 domain, we determined 13 psi angle constraints with the INADEQUATE NCCN experiment and 22 psi constraints were measured in the NCOCA NCCN experiment.

  7. Through-space (19) F-(15) N couplings for the assignment of stereochemistry in flubenzimine.

    PubMed

    Ghiviriga, Ion; Rubinski, Miles A; Dolbier, William R

    2016-07-01

    Through-space (19) F-(15) N couplings revealed the configuration of flubenzimine, with the CF3 group on N4 pointing towards the lone pair of N5. The (19) F-(15) N coupling constants were measured at natural abundance using a spin-state selective indirect-detection pulse sequence. As (15) N-labelled proteins are routinely synthesized for NMR studies, through-space (19) F-(15) N couplings have the potential to probe the stereochemistry of these proteins by (19) F labelling of some amino acids or can reveal the site of docking of fluorine-containing drugs. Copyright © 2016 John Wiley & Sons, Ltd.

  8. Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O.

    PubMed

    Vrábel, P; Orendáč, M; Orendáčová, A; Čižmár, E; Tarasenko, R; Zvyagin, S; Wosnitza, J; Prokleška, J; Sechovský, V; Pavlík, V; Gao, S

    2013-05-01

    We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O (bpdo=4, 4'-bipyridine-N,N'-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S = 1/2 and a weak exchange interaction J/kB = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd(3+) ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field. PMID:23587762

  9. Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O.

    PubMed

    Vrábel, P; Orendáč, M; Orendáčová, A; Čižmár, E; Tarasenko, R; Zvyagin, S; Wosnitza, J; Prokleška, J; Sechovský, V; Pavlík, V; Gao, S

    2013-05-01

    We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O (bpdo=4, 4'-bipyridine-N,N'-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S = 1/2 and a weak exchange interaction J/kB = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd(3+) ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field.

  10. One-Shot Measurement of Spin-Lattice Relaxation Times in the Off-Resonance Rotating Frame of Reference with Applications to Breast

    NASA Astrophysics Data System (ADS)

    Fairbanks, Ethan Jefferson

    1994-01-01

    Off-resonance spin locking makes use of the novel relaxation time T_{1rho} ^{rm off}, which may be useful in characterizing breast disease. Knowledge of T _{rm 1rho}^{rm off} is essential for optimization of spin -locking imaging methods. The purpose of this work was to develop an optimal imaging technique for in vivo measurement of T_{rm 1rho}^ {rm off}. Measurement of T _{1rho}^{rm off } using conventional methods requires long exam times which are not suitable for patients. Exam time may be shortened by utilizing a one-shot method developed by Look and Locker, making in vivo measurements possible. The imaging method consisted of a 180^circ inversion pulse followed by a series of small-angle alpha pulses to tip a portion of the longitudinal magnetization into the transverse plane for readout. During each relaxation interval (between alpha pulses), a spin-locking pulse was applied off-resonance to achieve T_ {1rho}^{rm off} relaxation. The value of T_{rm 1rho}^{rm off} was then determined using a three-parameter non-linear least-squares fitting procedure. Values of T_ {1rho}^{rm off} were measured for normal and pathologic breast tissues at several resonant offsets. These measurements revealed that image contrast can be manipulated by altering the resonant offset of the spin-locking pulse. Whereas T _1 relaxation times were nearly identical for normal and cancerous tissues, T_{1 rho}^{rm off} relaxation times differed significantly. These results may be useful in improving image contrast in magnetic resonance imaging.

  11. Studies of a Large Odd‐Numbered Odd‐Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8Mn

    PubMed Central

    Lancaster, Tom; Chiesa, Alessandro; Amoretti, Giuseppe; Baker, Peter J.; Barker, Claire; Carretta, Stefano; Collison, David; Güdel, Hans U.; Guidi, Tatiana; McInnes, Eric J. L.; Möller, Johannes S.; Mutka, Hannu; Ollivier, Jacques; Pratt, Francis L.; Santini, Paolo; Tuna, Floriana; Tregenna‐Piggott, Philip L. W.; Vitorica‐Yrezabal, Iñigo J.; Timco, Grigore A.

    2016-01-01

    Abstract The spin dynamics of Cr8Mn, a nine‐membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8Mn is a rare example of a large odd‐membered AF ring, and has an odd‐number of 3d‐electrons present. Odd‐membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated‐spin ground states. The chemical synthesis and structures of two Cr8Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground‐spin‐state crossing from S=1/2 to S=3/2 in Cr8Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin‐pair correlations and scalar‐spin chirality, shows a non‐collinear spin structure that fluctuates between non‐planar states of opposite chiralities. PMID:26748964

  12. In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect

    SciTech Connect

    Fang, Jiancheng; Wang, Tao Quan, Wei; Yuan, Heng; Li, Yang; Zhang, Hong; Zou, Sheng

    2014-06-15

    A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz{sup 1/2}, which was mainly dominated by the noise of the magnetic shield.

  13. In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect.

    PubMed

    Fang, Jiancheng; Wang, Tao; Quan, Wei; Yuan, Heng; Zhang, Hong; Li, Yang; Zou, Sheng

    2014-06-01

    A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz(1/2), which was mainly dominated by the noise of the magnetic shield.

  14. Interfacial membrane docking of cytosolic phospholipase A2 C2 domain using electrostatic potential-modulated spin relaxation magnetic resonance

    PubMed Central

    Ball, Andy; Nielsen, Robert; Gelb, Michael H.; Robinson, Bruce H.

    1999-01-01

    The C2 domain of cytosolic phospholipase A2 (C2cPLA2) plays an important role in calcium-dependent transfer of the protein from the cytosol to internal cellular membranes as a prelude for arachidonate release from membrane phospholipids. By using a recently developed electron paramagnetic resonance approach together with 13 site-specifically nitroxide spin labeled C2cPLA2s and membrane-permeant and -impermeant spin relaxants, we have determined the orientation of C2cPLA2 with respect to the surface of vesicles of the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphomethanol. The structure reveals that the two calcium-binding regions on C2cPLA2 that display hydrophobic residues, CBR1 and CBR3, are partially inserted into the core of the membrane. CBR2 that contains predominantly hydrophilic residues is close to the membrane but not inserted. The long axis of the cylindrical C2cPLA2 molecule is tilted with respect to the bilayer normal, which brings a cluster of basic protein residues close to the phospholipid headgroups. Such an orientation places the two bound calcium ions close to the membrane surface. All together, the results provide structural support for previous proposals that binding of C2cPLA2 to the membrane interface is driven in part by insertion of hydrophobic surface loops into the membrane core. The results are contrasted with previous studies of the interfacial binding of the first C2 domain of synaptotagmin I, which has shorter surface loops that display basic residues for electrostatic interaction with the bilayer surface. PMID:10359764

  15. Rotational dynamics in supercooled water from nuclear spin relaxation and molecular simulations.

    PubMed

    Qvist, Johan; Mattea, Carlos; Sunde, Erik P; Halle, Bertil

    2012-05-28

    Structural dynamics in liquid water slow down dramatically in the supercooled regime. To shed further light on the origin of this super-Arrhenius temperature dependence, we report high-precision (17)O and (2)H NMR relaxation data for H(2)O and D(2)O, respectively, down to 37 K below the equilibrium freezing point. With the aid of molecular dynamics (MD) simulations, we provide a detailed analysis of the rotational motions probed by the NMR experiments. The NMR-derived rotational correlation time τ(R) is the integral of a time correlation function (TCF) that, after a subpicosecond librational decay, can be described as a sum of two exponentials. Using a coarse-graining algorithm to map the MD trajectory on a continuous-time random walk (CTRW) in angular space, we show that the slowest TCF component can be attributed to large-angle molecular jumps. The mean jump angle is ∼48° at all temperatures and the waiting time distribution is non-exponential, implying dynamical heterogeneity. We have previously used an analogous CTRW model to analyze quasielastic neutron scattering data from supercooled water. Although the translational and rotational waiting times are of similar magnitude, most translational jumps are not synchronized with a rotational jump of the same molecule. The rotational waiting time has a stronger temperature dependence than the translation one, consistent with the strong increase of the experimentally derived product τ(R) D(T) at low temperatures. The present CTRW jump model is related to, but differs in essential ways from the extended jump model proposed by Laage and co-workers. Our analysis traces the super-Arrhenius temperature dependence of τ(R) to the rotational waiting time. We present arguments against interpreting this temperature dependence in terms of mode-coupling theory or in terms of mixture models of water structure. PMID:22667569

  16. Phase relaxed localized excitation pulses for inner volume fast spin echo imaging

    PubMed Central

    Hajnal, Joseph V.

    2015-01-01

    Purpose To design multidimensional spatially selective radiofrequency (RF) pulses for inner volume imaging (IVI) with three‐dimensional (3D) fast spin echo (FSE) sequences. Enhanced background suppression is achieved by exploiting particular signal properties of FSE sequences. Theory and Methods The CPMG condition dictates that echo amplitudes will rapidly decrease if a 90° phase difference between excitation and refocusing pulses is not present, and refocusing flip angles are not precisely 180°. This mechanism is proposed as a means for generating additional background suppression for spatially selective excitation, by biasing residual excitation errors toward violating the CPMG condition. 3D RF pulses were designed using this method with a 3D spherical spiral trajectory, under‐sampled by factor 5.6 for an eight‐channel PTx system, at 3 Tesla. Results 3D‐FSE IVI with pulse durations of approximately 12 ms was demonstrated in phantoms and for T2‐weighted brain imaging in vivo. Good image quality was obtained, with mean background suppression factors of 103 and 82 ± 6 in phantoms and in vivo, respectively. Conclusion Inner Volume Imaging with 3D‐FSE has been demonstrated in vivo with tailored 3D‐RF pulses. The proposed design methods are also applicable to 2D pulses. Magn Reson Med 76:848–861, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine PMID:26451691

  17. Muon Spin Relaxation Studies of Zn-Substitution Effects in High-{ital T{sub {ital c}}} Cuprate Superconductors

    SciTech Connect

    Nachumi, B.; Keren, A.; Kojima, K.; Larkin, M.; Luke, G.M.; Merrin, J.; Tchernyshoev, O.; Uemura, Y.J.; Ichikawa, N.; Goto, M.; Uchida, S.

    1996-12-01

    We have performed transverse-field muon spin relaxation measurements of the Zn-substituted cuprate high-{ital T}{sub {ital c}} superconductors: La{sub 2{minus}{ital x}}Sr{sub {ital x}}(Cu{sub 1{minus}{ital y}}Zn{sub {ital y}})O{sub 4} and YBa{sub 2}(Cu{sub 1{minus}{ital y}}Zn{sub {ital y}}){sub 3}O{sub 6.63}. The superconducting carrier density/effective mass {ital n}{sub {ital s}}/{ital m}{sup *} ratio at {ital T}{r_arrow}0 decreases with increasing Zn concentration, in a manner consistent with our {open_quote}{open_quote}swiss cheese{close_quote}{close_quote} model in which charge carriers within an area {pi}{xi}{sub {ital ab}}{sup 2} around each Zn are excluded from the superfluid. We discuss this result in the context of Bose condensation, pair localization, and pair breaking. {copyright} {ital 1996 The American Physical Society.}

  18. Safety Report - Experiments 999 and 891 Muon Spin Relaxation in Pu and Pu-based Heavy Fermion Materials

    SciTech Connect

    Fluss, M; Heffner, R; Morris, G

    2004-04-23

    Experiment E999 proposes to carry out conventional muon spin relaxation ({mu}SR) measurements on solid samples of plutonium and plutonium alloys. Experiment 891 will be involved with {mu}SR experiments on PuCoGa{sub 5} and related Pu-based superconductors. Other than a dedicated cryostat to be provided by Los Alamos and a pumping station provided by Livermore, the experiments will use existing {mu}SR User Facility spectrometers and associated equipment such as detectors and electronics. The main topics of this report are therefore (1) the passivation of the samples with a polymer coating, (2) the design, fabrication and testing of a sealed titanium sample secondary encapsulation cell, (3) the transport of samples to and from TRIUMF and (4) the related on-site procedures for the safe handling of the encapsulated samples. Because both E999 and E891 share the same equipment and Pu-safety related issues, we are submitting a single safety report for both experiments.

  19. Matrix deuteration effects and spin-lattice relaxation in the lowest triplet of the palladium(II) complex Pd(2-thpy) 2

    NASA Astrophysics Data System (ADS)

    Becker, Dirk; Yersin, Hartmut; von Zelewsky, Alex

    1995-03-01

    Pd(2-thpy) 2 isolated in protonated or deuterated frozen n-octane (Shpol'skii matrices) exhibits highly resolved triplet emission and excitation spectra. One observes interesting differences for the two matrices: (i) The protonated matrix shows only one dominant guest site while the deuterated matrix exhibits two dominant sites. (ii) Low-energy satellites corresponding to lattice modes are distinctly shifted to lower energy due to deuteration of the matrix, (iii) At 1.3 K the triplet sublevels emit independently with lifetimes being nearly equal for both matrices. However, for 1.3 < T < 5 K one observes obvious differences in the decay behavior. This is explained by substantially smaller rates of spin-lattice relaxation in the deuterated host. Different mechanisms of spin-lattice relaxation are discussed.

  20. Electron spin-lattice relaxation mechanisms of nitroxyl radicals in ionic liquids and conventional organic liquids: temperature dependence of a thermally activated process.

    PubMed

    Kundu, Krishnendu; Kattnig, Daniel R; Mladenova, Boryana Y; Grampp, Günter; Das, Ranjan

    2015-03-26

    During the past two decades, several studies have established a significant role played by a thermally activated process in the electron spin relaxation of nitroxyl free radicals in liquid solutions. Its role has been used to explain the spin relaxation behavior of these radicals in a wide range of viscosities and microwave frequencies. However, no temperature dependence of this process has been reported. In this work, our main aim was to investigate the temperature dependence of this process in neat solvents. Electron spin-lattice relaxation times of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-TEMPO (TEMPOL), in X-band microwave frequency, were measured by the pulse saturation recovery technique in three room-temperature ionic liquids ([bmim][BF4], [emim][BF4], and [bmim][PF6]), di-isononyl phthalate, and sec-butyl benzene. The ionic liquids provided a wide range of viscosity in a modest range of temperature. An auxiliary aim was to examine whether the dynamics of a probe molecule dissolved in ionic liquids was different from that in conventional molecular liquids, as claimed in several reports on fluorescence dynamics in ionic liquids. This was the reason for the inclusion of di-isononyl phthalate, whose viscosities are similar to that of the ionic liquids in similar temperatures, and sec-butyl benzene. Rotational correlation times of the nitroxyl radicals were determined from the hyperfine dependence of the electron paramagnetic resonance (EPR) line widths. Observation of highly well-resolved proton hyperfine lines, riding over the nitrogen hyperfine lines, in the low viscosity regime in all the solvents, gave more accurate values of the rotational correlation times than the values generally measured in the absence of these hyperfine lines and reported in the literature. The measured rotational correlation times obeyed a modified Stokes-Einstein-Debye relation of temperature dependence in all solvents. By separating the contributions of g

  1. Electron spin-lattice relaxation mechanisms of nitroxyl radicals in ionic liquids and conventional organic liquids: temperature dependence of a thermally activated process.

    PubMed

    Kundu, Krishnendu; Kattnig, Daniel R; Mladenova, Boryana Y; Grampp, Günter; Das, Ranjan

    2015-03-26

    During the past two decades, several studies have established a significant role played by a thermally activated process in the electron spin relaxation of nitroxyl free radicals in liquid solutions. Its role has been used to explain the spin relaxation behavior of these radicals in a wide range of viscosities and microwave frequencies. However, no temperature dependence of this process has been reported. In this work, our main aim was to investigate the temperature dependence of this process in neat solvents. Electron spin-lattice relaxation times of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-TEMPO (TEMPOL), in X-band microwave frequency, were measured by the pulse saturation recovery technique in three room-temperature ionic liquids ([bmim][BF4], [emim][BF4], and [bmim][PF6]), di-isononyl phthalate, and sec-butyl benzene. The ionic liquids provided a wide range of viscosity in a modest range of temperature. An auxiliary aim was to examine whether the dynamics of a probe molecule dissolved in ionic liquids was different from that in conventional molecular liquids, as claimed in several reports on fluorescence dynamics in ionic liquids. This was the reason for the inclusion of di-isononyl phthalate, whose viscosities are similar to that of the ionic liquids in similar temperatures, and sec-butyl benzene. Rotational correlation times of the nitroxyl radicals were determined from the hyperfine dependence of the electron paramagnetic resonance (EPR) line widths. Observation of highly well-resolved proton hyperfine lines, riding over the nitrogen hyperfine lines, in the low viscosity regime in all the solvents, gave more accurate values of the rotational correlation times than the values generally measured in the absence of these hyperfine lines and reported in the literature. The measured rotational correlation times obeyed a modified Stokes-Einstein-Debye relation of temperature dependence in all solvents. By separating the contributions of g

  2. Nuclear quadrupole spin-lattice relaxation in Bi{sub 4}Ge{sub 3}O{sub 12} single crystals doped with atoms of d or f elements. Crystal field effects in compounds exhibiting anomalous magnetic properties

    SciTech Connect

    Orlov, V. G. Sergeev, G. S.; Asaji, Tetsuo; Kravchenko, E. A.; Kargin, Yu. F.

    2010-02-15

    The nuclear quadrupole spin-lattice relaxation was studied in the range 4.2-300 K for single crystals of Bi{sub 4}Ge{sub 3}O{sub 12} doped with minor amounts (the tenth fractions of mol%) of paramagnetic atoms of Cr, Nd, and Gd. Unusual spin dynamic features were recently found for these crystals at room temperature: a dramatic (up to 8-fold) increase in the effective nuclear quadrupole spin-spin relaxation time T{sub 2}* occurred upon doping the pure Bi{sub 4}Ge{sub 3}O{sub 12} sample. Unlike T{sub 2}*, the effective spin-lattice relaxation time T{sub 1}* at room temperature differs insignificantly for both doped and pure samples. But at lower temperatures, the samples exhibit considerably different behavior of the spin-lattice relaxation with temperature, which is caused by different contributions to the relaxation process of the dopant paramagnetic atoms. The distinctive maximum in the temperature dependence of the spin-lattice relaxation time for the Nd-doped crystal is shown to result from the crystal electric field effects.

  3. The long-term post-outburst spin down and flux relaxation of magnetar swift J1822.3–1606

    SciTech Connect

    Scholz, P.; Kaspi, V. M.; Cumming, A.

    2014-05-01

    The magnetar Swift J1822.3–1606 entered an outburst phase in 2011 July. Previous X-ray studies of its post-outburst rotational evolution yielded inconsistent measurements of the spin-inferred magnetic field. Here we present the timing behavior and flux relaxation from over two years of Swift, RXTE, and Chandra observations following the outburst. We find that the ambiguity in previous timing solutions was due to enhanced spin down that resembles an exponential recovery following a glitch at the outburst onset. After fitting out the effects of the recovery, we measure a long-term spin-down rate of ν-dot =(−3.0 ± 0.3)×10{sup −16} s{sup –2} which implies a dipolar magnetic field of 1.35 × 10{sup 13} G, lower than all previous estimates for this source. We also consider the post-outburst flux evolution, and fit it with both empirical and crustal cooling models. We discuss the flux relaxation in the context of both crustal cooling and magnetospheric relaxation models.

  4. Elastic and anelastic relaxations accompanying magnetic ordering and spin-flop transitions in hematite, Fe2O3

    NASA Astrophysics Data System (ADS)

    Oravova, Lucie; Zhang, Zhiying; Church, Nathan; Harrison, Richard J.; Howard, Christopher J.; Carpenter, Michael A.

    2013-03-01

    Hematite, Fe2O3, provides in principle a model system for multiferroic (ferromagnetic/ferroelastic) behavior at low levels of strain coupling. The elastic and anelastic behavior associated with magnetic phase transitions in a natural polycrystalline sample have therefore been studied by resonant ultrasound spectroscopy (RUS) in the temperature range from 11 to 1072 K. Small changes in softening and attenuation are interpreted in terms of weak but significant coupling of symmetry-breaking and non-symmetry-breaking strains with magnetic order parameters in the structural sequence R\\overline{3}c{1}^{\\prime}\\rightarrow C 2/c\\rightarrow R\\overline{3}c. The R\\overline{3}c{1}^{\\prime}\\rightarrow C 2/c transition at TN = 946 ± 1 K is an example of a multiferroic transition which has both ferromagnetic (from canting of antiferromagnetically ordered spin moments) and ferroelastic (rhombohedral → monoclinic) character. By analogy with the improper ferroelastic transition in Pb3(PO4)2, W and W‧ ferroelastic twin walls which are also 60° and 120° magnetic domain walls should develop. These have been tentatively identified from microstructures reported in the literature. The very low attenuation in the stability field of the C2/c structure in the polycrystalline sample used in the present study, in comparison with the strong acoustic dissipation reported for single crystal samples, implies, however, that the individual grains each consist of a single ferroelastic domain or that the twin walls are strongly pinned by grain boundaries. This absence of attenuation allows an intrinsic loss mechanism associated with the transition point to be seen and interpreted in terms of local coupling of shear strains with fluctuations which have relaxation times in the vicinity of ˜10-8 s. The first order C 2/c\\rightarrow R\\overline{3}c (Morin) transition occurs through a temperature interval of coexisting phases but the absence of an acoustic loss peak suggests that the

  5. 1H and 19F spin-lattice relaxation and CH3 or CF3 reorientation in molecular solids containing both H and F atoms

    NASA Astrophysics Data System (ADS)

    Beckmann, Peter A.; Rheingold, Arnold L.

    2016-04-01

    The dynamics of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state 1H and 19F spin-lattice relaxation experiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF3 reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance (NMR) time scale) to investigate CF3 reorientation occurring on the NMR time scale. The effects of 19F-19F and 19F-1H spin-spin dipolar interactions on the complicated nonexponential NMR relaxation provide independent inputs into determining a model for CF3 reorientation. As such, these experiments provide much more information than when only one spin species (usually 1H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH3 and CF3 reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components.

  6. Single-shot readout and relaxation of singlet and triplet states in exchange-coupled 31P electron spins in silicon.

    PubMed

    Dehollain, Juan P; Muhonen, Juha T; Tan, Kuan Y; Saraiva, Andre; Jamieson, David N; Dzurak, Andrew S; Morello, Andrea

    2014-06-13

    We present the experimental observation of a large exchange coupling J ≈ 300 μeV between two (31)P electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a single-electron transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time T(1) ≈ 4 ms at zero magnetic field agrees with the theoretical prediction for J-coupled 31P dimers in silicon. The time evolution of the two-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of two-qubit quantum logic gates with spins in silicon and highlight the necessity to adopt gating schemes compatible with weak J-coupling strengths. PMID:24972221

  7. Single-shot readout and relaxation of singlet and triplet states in exchange-coupled 31P electron spins in silicon.

    PubMed

    Dehollain, Juan P; Muhonen, Juha T; Tan, Kuan Y; Saraiva, Andre; Jamieson, David N; Dzurak, Andrew S; Morello, Andrea

    2014-06-13

    We present the experimental observation of a large exchange coupling J ≈ 300 μeV between two (31)P electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a single-electron transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time T(1) ≈ 4 ms at zero magnetic field agrees with the theoretical prediction for J-coupled 31P dimers in silicon. The time evolution of the two-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of two-qubit quantum logic gates with spins in silicon and highlight the necessity to adopt gating schemes compatible with weak J-coupling strengths.

  8. Geometric Magnetic Frustration in Li3Mg2OsO6 Studied with Muon Spin Relaxation

    NASA Astrophysics Data System (ADS)

    Carlo, J. P.; Derakhshan, S.; Greedan, J. E.

    Geometric frustration manifests when the spatial arrangement of ions inhibits magnetic order. Typically associated with antiferromagnetically (AF)-correlated moments on triangular or tetrahedral lattices, frustration occurs in a variety of structures and systems, resulting in rich phase diagrams and exotic ground states. As a window to exotic physics revealed by the cancellation of normally dominant interactions, the research community has taken great interest in frustrated systems. One family of recent interest are the rock-salt ordered oxides A5BO6, in which the B sites are occupied by magnetic ions comprising a network of interlocked tetrahedra, and nonmagnetic ions on the A sites control the B oxidation state through charge neutrality. Here we will discuss studies of Li3Mg2OsO6 using muon spin relaxation (μSR), a highly sensitive local probe of magnetism. Previous studies of this family included Li5OsO6, which exhibits AF order below 50K with minimal evidence for frustration, and Li4MgReO6, which exhibits glassy magnetism. Li3Mg2RuO6, meanwhile, exhibits long-range AF, with the ordering temperature suppressed by frustration. But its isoelectronic twin, Li3Mg2OsO6 (5d3 vs. 4d3) exhibits very different behavior, revealed by μSR to be a glassy ground state below 12K. Understanding why such similar systems exhibit diverse ground-state behavior is key to understanding the nature of geometric magnetic frustration. Financial support from the Research Corporation for Science Advancement.

  9. (77)Se nuclear spin-lattice relaxation in binary Ge-Se glasses: insights into floppy versus rigid behavior of structural units.

    PubMed

    Sen, Sabyasachi; Kaseman, Derrick C; Hung, Ivan; Gan, Zhehong

    2015-04-30

    The mechanism of (77)Se nuclear spin-lattice relaxation is investigated in binary Ge-Se glasses. The (77)Se nuclides in Se-Se-Se chain sites relax faster via dipolar coupling fluctuation compared to those in Ge-Se-Ge sites shared by GeSe4 tetrahedra that relax slower via the fluctuation of the chemical shift anisotropy. The relaxation rate for the Se-Se-Se sites decreases markedly with increasing magnetic field, whereas that for the Ge-Se-Ge sites displays no appreciable dependence on the magnetic field such that the extent of differential relaxation between the two Se environments becomes small at high fields on the order of 19.6 T. The corresponding dynamical correlation time is three orders of magnitude shorter (∼10(-9) s) for the Se-Se-Se sites, compared to that for the Ge-Se-Ge sites (∼10(-6) s). The large decoupling in the time scale between these Se environments provides direct experimental support to the commonly made assumption that the selenium chains are mechanically floppy, and the interconnected GeSe4 tetrahedra form the rigid elements in the selenide glass structure.

  10. 15N chemical shift referencing in solid state NMR.

    PubMed

    Bertani, Philippe; Raya, Jésus; Bechinger, Burkhard

    2014-01-01

    Solid-state NMR spectroscopy has much advanced during the last decade and provides a multitude of data that can be used for high-resolution structure determination of biomolecules, polymers, inorganic compounds or macromolecules. In some cases the chemical shift referencing has become a limiting factor to the precision of the structure calculations and we have therefore evaluated a number of methods used in proton-decoupled (15)N solid-state NMR spectroscopy. For (13)C solid-state NMR spectroscopy adamantane is generally accepted as an external standard, but to calibrate the (15)N chemical shift scale several standards are in use. As a consequence the published chemical shift values exhibit considerable differences (up to 22 ppm). In this paper we report the (15)N chemical shift of several commonly used references compounds in order to allow for comparison and recalibration of published data and future work. We show that (15)NH4Cl in its powdered form (at 39.3 ppm with respect to liquid NH3) is a suitable external reference as it produces narrow lines when compared to other reference compounds and at the same time allows for the set-up of cross-polarization NMR experiments. The compound is suitable to calibrate magic angle spinning and static NMR experiments. Finally the temperature variation of (15)NH4Cl chemical shift is reported.

  11. Host spin-lattice relaxation narrowing and the electron paramagnetic resonance of Mn(II) in single crystals of hexakis(pyridine N-oxide)cobalt(II) complexes

    NASA Astrophysics Data System (ADS)

    Murugesan, R.; Thamaraichelvan, A.; Milton Franklin, A.; Ramakrishnan, V.

    The electron paramagnetic resonance spectra of Mn(C5H5NO)6. X2 (X ≡ ClO-4, BF-4 and NO-3) doped in single crystals of isomorphous paramagnetic Co(C5H5NO)6. X2 are studied at various temperatures. Zero-field splitting in all three crystals is axially symmetric and the magnitude of D is unusually large for an octahedral coordination polyhedron with all ligands identical. The sharp resonance of Mn(II) in the paramagnetic host observed at high temperatures is interpreted in terms of random modulation of the dipolar interaction between the guest Mn(II) and host Co(II) ions by the rapid spin-lattice relaxation of Co(II). The spin-lattice relaxation times of Co(II) ions at 300 K, estimated from the temperature dependent linewidth of the Mn(II) resonance, are 24 × 10-12, 28 × 10-12 and 23 × 10-12 s in perchlorate, fluoborate and nitrate crystals respectively. The temperature dependence of the relaxation is of the form 1/(at + bt5) and below 270 K the direct process dominates.

  12. Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C 7H 6N 2O 6)(H 2O) 3·2H 2O

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.

    2000-11-01

    In response to recent nuclear magnetic resonance measurements on a ferrimagnetic chain compound NiCu(C 7H 6N 2O 6)(H 2O) 3·2H 2O [Solid State Commun. 113 (2000) 433], we calculate the nuclear spin-lattice relaxation rate 1/ T1 in terms of a modified spin-wave theory. Emphasizing that the dominant relaxation mechanism arises from the direct (single-magnon) process rather than the Raman (two-magnon) one, we explain the observed temperature and applied-field dependences of 1/ T1. Ferrimagnetic relaxation phenomena are generally discussed and novel ferrimagnets with extremely slow dynamics are predicted.

  13. Impact of neonate haematocrit variability on the longitudinal relaxation time of blood: Implications for arterial spin labelling MRI

    PubMed Central

    De Vis, J.B.; Hendrikse, J.; Groenendaal, F.; de Vries, L.S.; Kersbergen, K.J.; Benders, M.J.N.L.; Petersen, E.T.

    2014-01-01

    Background and purpose The longitudinal relaxation time of blood (T1b) is influenced by haematocrit (Hct) which is known to vary in neonates. The purpose of this study was threefold: to obtain T1b values in neonates, to investigate how the T1b influences quantitative arterial spin labelling (ASL), and to evaluate if known relationships between T1b and haematocrit (Hct) hold true when Hct is measured by means of a point-of-care device. Materials and methods One hundred and four neonates with 120 MR scan sessions (3 T) were included. The T1b was obtained from a T1 inversion recovery sequence. T1b-induced changes in ASL cerebral blood flow estimates were evaluated. The Hct was obtained by means of a point-of-care device. Linear regression analysis was used to investigate the relation between Hct and MRI-derived R1 of blood (the inverse of the T1b). Results Mean T1b was 1.85 s (sd 0.2 s). The mean T1b in preterm neonates was 1.77 s, 1.89 s in preterm neonates scanned at term-equivalent age (TEA) and 1.81 s in diseased neonates. The T1b in the TEA was significantly different from the T1b in the preterm (p < 0.05). The change in perfusion induced by the T1b was −11% (sd 9.1%, p < 0.001). The relation between arterial-drawn Hct and R1b was R1b = 0.80 × Hct + 0.22, which falls within the confidence interval of the previously established relationships, whereas capillary-drawn Hct did not correlate with R1b. Conclusion We demonstrated a wide variability of the T1b in neonates and the implications it could have in methods relying on the actual T1b as for instance ASL. It was concluded that arterial-drawn Hct values obtained from a point-of-care device can be used to infer the T1b whereas our data did not support the use of capillary-drawn Hct for T1b correction. PMID:24818078

  14. Tuning of the hole spin relaxation time in single self-assembled In{sub 1−x}Ga{sub x}As/GaAs quantum dots by electric field

    SciTech Connect

    Wei, Hai; Guo, Guang-Can; He, Lixin

    2014-11-28

    We investigate the electric field tuning of the phonon-assisted hole spin relaxation in single self-assembled In{sub 1−x}Ga{sub x}As/GaAs quantum dots (QDs), using an atomistic empirical pseudopotential method. We find that the electric field along the growth direction can tune the hole spin relaxation time for more than one order of magnitude. The electric field can prolong or shorten the hole spin lifetime and the tuning shows an asymmetry in terms of the field direction. The asymmetry is more pronounced for the taller dot. The results show that the electric field is an effective way to tune the hole spin-relaxation in self-assembled QDs.

  15. Is the manifestation of the local dynamics in the spin-lattice NMR relaxation in dendrimers sensitive to excluded volume interactions?

    PubMed

    Shavykin, Oleg V; Neelov, Igor M; Darinskii, Anatolii A

    2016-09-21

    The effect of excluded volume (EV) interactions on the manifestation of the local dynamics in the spin-lattice NMR relaxation in dendrimers has been studied by using Brownian dynamics simulations. The study was motivated by the theory developed by Markelov et al., [J. Chem. Phys., 2014, 140, 244904] for a Gaussian dendrimer model without EV interactions. The theory connects the experimentally observed dependence of the spin-lattice relaxation rate 1/T(1)H on the location of NMR active groups with the restricted flexibility (semiflexibility) of dendrimers. Semiflexibility was introduced through the correlations between the orientations of different segments. However, these correlations exist even in flexible dendrimer models with EV interactions. We have simulated coarse-grained flexible and semiflexible dendrimer models with and without EV interactions. Every dendrimer segment consisted of two rigid bonds. Semiflexibility was introduced through a potential which restricts the fluctuations of angles between neighboring bonds but does not change orientational correlations in the EV model as compared to the flexible case. The frequency dependence of the reduced 1/T(1)H(ωH) for segments and bonds belonging to different dendrimer shells was calculated. It was shown that the main effect of EV interactions consists of a much stronger contribution of the overall dendrimer rotation to the dynamics of dendrimer segments as compared to phantom models. After the exclusion of this contribution the manifestation of internal dynamics in spin-lattice NMR relaxation appears to be practically insensitive to EV interactions. For the flexible models, the position ωmax of the peak of the modified 1/T(1)H(ωH) does not depend on the shell number. For semiflexible models, the maximum of 1/T(1)H(ωH) for internal segments or bonds shifts to lower frequencies as compared to outer ones. The dependence of ωmax on the number of dendrimer shells appears to be universal for segments and

  16. Spin-lattice relaxation and ODMR linenarrowing of the photoexcited triplet state of pyrene in polycrystalline Shpol'skii hosts and glassy matrices

    NASA Astrophysics Data System (ADS)

    Tringali, Arthur E.; Brenner, Henry C.

    1998-01-01

    Phosphorescence and ODMR linewidths, and spin-lattice relaxation (SLR) rates were measured at pumped helium temperatures for the triplet excited state of pyrene doped in several n-alkane polycrystalline hosts as well as in 3-methylpentane (3-MP) glass, in order to test the expectation that the optimum Shpol'skii matrix for pyrene should lead to the slowest SLR rates. Among the series of n-alkanes, n-hexane showed the best Shpol'skii effect for pyrene in terms of the narrowest phosphorescence and weakest guest-host phonon coupling. The 2| E| and | D+ E| ODMR linewidths for pyrene were minimized in n-hexane as well. Microwave saturated phosphorescence decay and fast passage methods were used to measure the SLR rates in the range 1.75-4.2 K. SLR appeared to be slowest in n-octane rather than n-hexane, but was significantly faster in n-decane and 3-MP. A marked anisotropy was observed in all hosts, in which the in-plane ( x ⇄  y) relaxation rate was 20-40 times the other rates. While this was suggestive of a mechanism in which SLR occurs by means of thermal promotion to a local phonon state with rotated spin axes, the observed activation energy was too small (2-3 cm -1) to be consistent with such a mechanism. In n-hexane, the relaxation appears to proceed by means of a direct process (rate αT1) in this temperature range. In the 3-MP glass, relaxation was faster than in the polycrystalline hosts, and followed a power law temperature dependence with an exponent of 2.4±0.2, in agreement with earlier studies of naphthalene derivatives in the same host, indicating that a direct two-level-system phonon mechanism is important in this glassy host.

  17. Unconventional Superconductivity in La7Ir3 Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry

    NASA Astrophysics Data System (ADS)

    Barker, J. A. T.; Singh, D.; Thamizhavel, A.; Hillier, A. D.; Lees, M. R.; Balakrishnan, G.; Paul, D. McK.; Singh, R. P.

    2015-12-01

    The superconductivity of the noncentrosymmetric compound La7 Ir3 is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature Tc=2.25 K —a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La7 Ir3 may be unconventional and paves the way for further studies of this family of materials.

  18. Muon-spin relaxation study of the double perovskite insulators Sr2 BOsO6 (B  =  Fe, Y, ln).

    PubMed

    Williams, R C; Xiao, F; Thomas, I O; Clark, S J; Lancaster, T; Cornish, G A; Blundell, S J; Hayes, W; Paul, A K; Felser, C; Jansen, M

    2016-02-24

    We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2 BOsO6 (B = Fe,Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below [Formula: see text] K. Upon cooling below T2≈67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below TN = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.

  19. On-site monitoring of atomic density number for an all-optical atomic magnetometer based on atomic spin exchange relaxation.

    PubMed

    Zhang, Hong; Zou, Sheng; Chen, Xiyuan; Ding, Ming; Shan, Guangcun; Hu, Zhaohui; Quan, Wei

    2016-07-25

    We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature. PMID:27464172

  20. On-site monitoring of atomic density number for an all-optical atomic magnetometer based on atomic spin exchange relaxation.

    PubMed

    Zhang, Hong; Zou, Sheng; Chen, Xiyuan; Ding, Ming; Shan, Guangcun; Hu, Zhaohui; Quan, Wei

    2016-07-25

    We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature.

  1. Proton and deuterium nuclear spin relaxation study of the SmA and SmC* phases of BP8Cl-d17 : a self-consistent analysis.

    PubMed

    Ferraz, A; Zhang, J; Sebastião, P J; Ribeiro, A C; Dong, Ronald Y

    2014-10-01

    A self-consistent analysis of proton and deuterium nuclear spin relaxation times in the smectic phases of a partially deuterated smectogen is presented here. Proton spin-lattice relaxation times T(1Z) were measured as a function of Larmor frequency over a range of 1 kHz to 300 MHz at selected temperatures. Deuterium spin relaxation times T(1Z) and T(1Q) were measured as a function of temperature at two different magnetic fields in the smectic A phase. The deuterium data provide dynamic parameters such as rotational diffusion constants and internal jump rates as well as the nematic order parameter S. The proton data are analyzed using a number of relaxation mechanisms, one of which is the molecular reorientation. It is found helpful in these latter analyses to use the nematic order parameter and to fix the contribution from molecular reorientations determined by the deuterium spin relaxation. The fits to the proton T(1) frequency and temperature dispersions by the remaining relaxation mechanisms such as layer undulations and translational self-diffusion will be discussed for the smectic A and chiral smectic C phases.

  2. Polymer dynamics near the surface and in the bulk of poly(tetrafluoroethylene) probed by zero-field muon-spin-relaxation spectroscopy.

    PubMed

    McKenzie, Iain; Salman, Zaher; Giblin, Sean R; Han, Yun Yu; Leach, Gary W; Morenzoni, Elvezio; Prokscha, Thomas; Suter, Andreas

    2014-02-01

    The results of many experiments on polymers such as polystyrene indicate that the polymer chains near a free surface exhibit enhanced dynamics when compared with the bulk. We have investigated whether this is the case for poly(tetrafluoroethylene) (PTFE) by using zero-field muon-spin-relaxation spectroscopy to characterize a local probe, the F-Mu(+)-F state, which forms when spin-polarized positive muons are implanted in PTFE. Low-energy muons (implantation energies from 2.0 to 23.0 keV) were used to study the F-Mu(+)-F state between ∼ 23 and 191 nm from the free surface of PTFE. Measurements were also made with surface muons (4.1 MeV) where the mean implantation depth is on the order of ∼ 0.6 mm. The relaxation rate of the F-Mu(+)-F state up to ∼ 150 K was found to be significantly higher for muons implanted at 2.0 keV than for higher implantation energies, which suggests that the polymer chains in a region on the order of a few tens of nanometers from the free surface are more mobile than those in the bulk.

  3. Lattice sites, charge states and spin-lattice relaxation of Fe ions in 57Mn+ implanted GaN and AlN

    NASA Astrophysics Data System (ADS)

    Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Gunnlaugsson, H. P.; Johnston, K.; Mantovan, R.; Mølholt, T. E.; Ncube, M.; Shayestehaminzadeh, S.; Gíslason, H. P.; Langouche, G.; Ólafsson, S.; Weyer, G.

    2016-03-01

    The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe ions in GaN and AlN were investigated by emission Mössbauer spectroscopy following the implantation of radioactive 57Mn+ ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV γ-rays from the 57Fe Mössbauer state (populated from the 57Mn β- decay) reveal that the majority of the Fe ions are in the 2+ valence state nearly substituting the Ga and Al cations, and/or associated with vacancy type defects. Emission Mössbauer spectroscopy experiments conducted over a temperature range of 100-800 K show the presence of magnetically split sextets in the "wings" of the spectra for both materials. The temperature dependence of the sextets relates these spectral features to paramagnetic Fe3+ with rather slow spin-lattice relaxation rates which follow a T2 temperature dependence characteristic of a two-phonon Raman process.

  4. Polymer dynamics near the surface and in the bulk of poly(tetrafluoroethylene) probed by zero-field muon-spin-relaxation spectroscopy.

    PubMed

    McKenzie, Iain; Salman, Zaher; Giblin, Sean R; Han, Yun Yu; Leach, Gary W; Morenzoni, Elvezio; Prokscha, Thomas; Suter, Andreas

    2014-02-01

    The results of many experiments on polymers such as polystyrene indicate that the polymer chains near a free surface exhibit enhanced dynamics when compared with the bulk. We have investigated whether this is the case for poly(tetrafluoroethylene) (PTFE) by using zero-field muon-spin-relaxation spectroscopy to characterize a local probe, the F-Mu(+)-F state, which forms when spin-polarized positive muons are implanted in PTFE. Low-energy muons (implantation energies from 2.0 to 23.0 keV) were used to study the F-Mu(+)-F state between ∼ 23 and 191 nm from the free surface of PTFE. Measurements were also made with surface muons (4.1 MeV) where the mean implantation depth is on the order of ∼ 0.6 mm. The relaxation rate of the F-Mu(+)-F state up to ∼ 150 K was found to be significantly higher for muons implanted at 2.0 keV than for higher implantation energies, which suggests that the polymer chains in a region on the order of a few tens of nanometers from the free surface are more mobile than those in the bulk. PMID:25353500

  5. HCN, A Triple-Resonance NMR Technique for Selective Observation of Histidine and Tryptophan Side Chains in 13C/ 15N-Labeled Proteins

    NASA Astrophysics Data System (ADS)

    Sudmeier, James L.; Ash, Elissa L.; Günther, Ulrich L.; Luo, Xuelian; Bullock, Peter A.; Bachovchin, William W.

    1996-12-01

    HCN, a new 3D NMR technique for stepwise coherence transfer from1H to13C to15N and reverse through direct spin couplings1JCHand1JCN, is presented as a method for detection and assignment of histidine and tryptophan side-chain1H,13C, and15N resonances in uniformly13C/15N-labeled proteins. Product-operator calculations of cross-peak volumes vs adjustable delay τ3were employed for determination of optimal τ3. For the phosphatidylinositol 3-kinase (PI3K SH3 domain, MW = 9.6 kD) at pH 6, H(C)N, the1H/15N projection, produced observable cross peaks within 20 min. and was completely selective for the single tryptophan and single histidine. The 3D HCN experiment yielded well-defined cross peaks in 20 h for the13C/15N-labeled origin-specific DNA binding domain from simian virus 40 T-antigen (T-ag-OBD131-259, MW = 15.4 kD) at pH 5.5. Resonances from all six histidines in T-ag-OBD were observed, and 11 of the 121H and13C chemical shifts and 10 of the 1215N chemical shifts were determined. The13C dimension proved essential in assignment of the multiply overlapping1H and15N resonances. From the spectra recorded at a single pH, three of the imidazoles were essentially neutral and the other three were partially protonated (22-37%). HCN yielded strong cross peaks after 18 h on a 2.0 mMsample of phenylmethanesulfonyl fluoride (PMSF)-inhibited α-lytic protease (MW = 19.8 kD) at pH 4.4. No spectra have been obtained, however, of native or boronic acid-inhibited α-lytic protease after 18 h at various temperatures ranging from 5 to 55°C, probably due to efficient relaxation of active-site imidazole1H and/or15N nuclei.

  6. Magnetic Field-Independent ^17O and ^63, 65Cu Normal State Spin Lattice Relaxation as Inferred by ^17O T2 NMR up to 28 T in YBa_2Cu_3O_7

    NASA Astrophysics Data System (ADS)

    Mitrovic, V. F.; Bachman, H. N.; Halperin, W. P.

    1998-03-01

    ^17O spin-spin relaxation NMR (T_2) is a powerful probe of vortex fluctuations in high Tc cuprates.(H. N. Bachman et al)., Bull. Am. Phys. Soc., 41, 467 (1996). It is important to understand the normal state T2 relaxation in order to extract the vortex field fluctuations.^1,(C. H. Recchia et al)., Phys. Rev. Lett. 78, 3543 (1997). The study of T2 in YBCO has shown that, in the normal state, copper and oxygen spin fluctuations (T1 processes) dominate the time scales for T_2, the spin-echo height decay. Thus, measurements of T2 as a function of magnetic field are an indicator of ^17O and ^63, 65Cu T1 behavior. We report new T2 measurements taken in the normal state from 3.2 T up to 28.2 T in which the spin-spin relaxation rate is observed to be completely field independent. By comparison with the predicted spin echo height decay given by the Gaussian Phase Approximation model we show that T1 of ^63, 65Cu and ^17O must not deviate from their published low-field values, within experimental error, over the entire magnetic field range. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity. The NHMFL is supported through the NSF and the state of Florida.

  7. Hydrogen doppler spectroscopy using 15N ions

    NASA Astrophysics Data System (ADS)

    Borucki, L.; Becker, H. W.; Gorris, F.; Kubsky, S.; Schulte, W. H.; Rolfs, C.

    The energy spread of atomic and molecular ion beams from the 4 MV Dynamitron tandem accelerator at the Ruhr-Universität Bochum has been studied and in part minimized. Using the ER= 6.40 MeV narrow resonance in 1H(15N,αγ)12C with an 15N energy spread of 4.55 keV, the Doppler broadening for several hydrogen-bearing gases was found to be in good agreement with expectation: e.g. for NH3 gas a rotational-vibrational Doppler width of 10.41 +/- 0.25 keV was observed (theory = 10.4 keV). Studies of the vibrational Doppler widths of H-bonds on a Si <100> surface were performed using a 4πγ-ray detection system together with UHV-chambers for sample preparation, transport, and analysis. The results showed that further improvements in the experimental set-ups are needed for such investigations.

  8. Is the manifestation of the local dynamics in the spin-lattice NMR relaxation in dendrimers sensitive to excluded volume interactions?

    PubMed

    Shavykin, Oleg V; Neelov, Igor M; Darinskii, Anatolii A

    2016-09-21

    The effect of excluded volume (EV) interactions on the manifestation of the local dynamics in the spin-lattice NMR relaxation in dendrimers has been studied by using Brownian dynamics simulations. The study was motivated by the theory developed by Markelov et al., [J. Chem. Phys., 2014, 140, 244904] for a Gaussian dendrimer model without EV interactions. The theory connects the experimentally observed dependence of the spin-lattice relaxation rate 1/T(1)H on the location of NMR active groups with the restricted flexibility (semiflexibility) of dendrimers. Semiflexibility was introduced through the correlations between the orientations of different segments. However, these correlations exist even in flexible dendrimer models with EV interactions. We have simulated coarse-grained flexible and semiflexible dendrimer models with and without EV interactions. Every dendrimer segment consisted of two rigid bonds. Semiflexibility was introduced through a potential which restricts the fluctuations of angles between neighboring bonds but does not change orientational correlations in the EV model as compared to the flexible case. The frequency dependence of the reduced 1/T(1)H(ωH) for segments and bonds belonging to different dendrimer shells was calculated. It was shown that the main effect of EV interactions consists of a much stronger contribution of the overall dendrimer rotation to the dynamics of dendrimer segments as compared to phantom models. After the exclusion of this contribution the manifestation of internal dynamics in spin-lattice NMR relaxation appears to be practically insensitive to EV interactions. For the flexible models, the position ωmax of the peak of the modified 1/T(1)H(ωH) does not depend on the shell number. For semiflexible models, the maximum of 1/T(1)H(ωH) for internal segments or bonds shifts to lower frequencies as compared to outer ones. The dependence of ωmax on the number of dendrimer shells appears to be universal for segments and

  9. Site-specific φ- and ψ-torsion angle determination in a uniformly/extensively 13C- and 15N-labeled peptide

    NASA Astrophysics Data System (ADS)

    Wi, Sungsool; Spano, Justin

    2011-10-01

    A solid-state rotational-echo double resonance (REDOR) NMR method was introduced to identify the ϕ- and ψ-torsion angle from a 1H- 15N or 1H- 13C' spin system of alanine-like residues in a selectively, uniformly, or extensively 15N-/ 13C-labeled peptide. When a C α( i) or a 15N peak is site-specifically obtainable in the NMR spectrum of a uniformly 15N/ 13C-labeled sample system, the ψ- or ϕ-torsion angle specified by the conformational structure of peptide geometry involving 15N( i)- 1H αi - 15N( i + 1) or 13C'( i - 1)- 1H Ni- 13C'( i) spin system can be identified based on 13C α- or 15N-detected 1H α- 15N or 1H N- 13C REDOR experiment. This method will conveniently be utilized to identify major secondary motifs, such as α-helix, β-sheet, and β-turn, from a uniformly 15N-/ 13C-labled peptide sample system. When tested on a 13C-/ 15N-labeled model system of a three amino acid peptide Gly-[U- 13C, 15N]Ala-[U- 13C, 15N]Leu, the ψ-angle of alanine obtained experimentally, ψ = -40 ± 30°, agreed reasonably well with the X-ray determined angle, ψ = -39°.

  10. Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry.

    PubMed

    Barker, J A T; Singh, D; Thamizhavel, A; Hillier, A D; Lees, M R; Balakrishnan, G; Paul, D McK; Singh, R P

    2015-12-31

    The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials. PMID:26765016

  11. 11B and 27Al NMR spin-lattice relaxation and Knight shift of Mg1-xAlxB2: Evidence for an anisotropic Fermi surface

    NASA Astrophysics Data System (ADS)

    Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.

    2002-10-01

    We report a detailed study of the 11B and 27Al NMR spin-lattice relaxation rates (1/T1) and the 27Al Knight shift (K) in Mg1-xAlxB2, 0<=x<=1. The evolution of (1/T1T) and K with x is in excellent agreement with the prediction of ab initio calculations of a highly anisotropic Fermi surface, consisting mainly of hole-type two-dimensional (2D) cylindrical sheets from bonding 2px,y boron orbitals. The density of states at the Fermi level also decreases sharply on Al doping and the 2D sheets collapse at x~0.55, where the superconducting phase disappears.

  12. Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry.

    PubMed

    Barker, J A T; Singh, D; Thamizhavel, A; Hillier, A D; Lees, M R; Balakrishnan, G; Paul, D McK; Singh, R P

    2015-12-31

    The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials.

  13. ESR Study of Electron-Nuclear Dipolar Relaxation for AsO 44-Spin Probe in the Paraelectric Phase of KH 2AsO 4

    NASA Astrophysics Data System (ADS)

    Rakvin, B.; Merunka, D.

    1997-05-01

    Saturation behavior of allowed and forbidden ESR transition of AsO44-paramagnetic probe in KH2AsO4was studied in the wide temperature interval around the paraelectric-ferroelectric phase transition,Tc. The ratios between forbidden and allowed line intensities were employed to deduce information on the electron-nuclear dipolar (END) relaxation mechanism. It was shown that a proton END relaxation mechanism exhibits an extremal temperature behavior in the paraelectric phase around 230 K. The extremal temperature behavior was described by employing a model of proton hopping along the O-H···O bonds around the paramagnetic centers, and the correlation time of this hopping was estimated in the wide temperature range in the paraelectric phase (150-330 K). The temperature dependence of effective proton distance from the neighbor oxygens was obtained, and it was discussed in terms of a localization of the spin density on these oxygens caused by charge inbalance in the As-O bonds in the ferroelectric phase.

  14. Muon-spin relaxation study of the double perovskite insulators Sr2 BOsO6 (B  =  Fe, Y, ln).

    PubMed

    Williams, R C; Xiao, F; Thomas, I O; Clark, S J; Lancaster, T; Cornish, G A; Blundell, S J; Hayes, W; Paul, A K; Felser, C; Jansen, M

    2016-02-24

    We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2 BOsO6 (B = Fe,Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below [Formula: see text] K. Upon cooling below T2≈67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below TN = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively. PMID:26807612

  15. Membrane Docking Geometry of GRP1 PH Domain Bound to a Target Lipid Bilayer: An EPR Site-Directed Spin-Labeling and Relaxation Study

    PubMed Central

    Landgraf, Kyle E.; Corbin, John A.; Falke, Joseph J.

    2012-01-01

    The second messenger lipid PIP3 (phosphatidylinositol-3,4,5-trisphosphate) is generated by the lipid kinase PI3K (phosphoinositide-3-kinase) in the inner leaflet of the plasma membrane, where it regulates a broad array of cell processes by recruiting multiple signaling proteins containing PIP3-specific pleckstrin homology (PH) domains to the membrane surface. Despite the broad importance of PIP3-specific PH domains, the membrane docking geometry of a PH domain bound to its target PIP3 lipid on a bilayer surface has not yet been experimentally determined. The present study employs EPR site-directed spin labeling and relaxation methods to elucidate the membrane docking geometry of GRP1 PH domain bound to bilayer-embedded PIP3. The model target bilayer contains the neutral background lipid PC and both essential targeting lipids: (i) PIP3 target lipid that provides specificity and affinity, and (ii) PS facilitator lipid that enhances the PIP3 on-rate via an electrostatic search mechanism. The EPR approach measures membrane depth parameters for 18 function-retaining spin labels coupled to the PH domain, and for calibration spin labels coupled to phospholipids. The resulting depth parameters, together with the known high resolution structure of the co-complex between GRP1 PH domain and the PIP3 headgroup, provide sufficient constraints to define an optimized, self-consistent membrane docking geometry. In this optimized geometry the PH domain engulfs the PIP3 headgroup with minimal bilayer penetration, yielding the shallowest membrane position yet described for a lipid binding domain. This binding interaction displaces the PIP3 headgroup from its lowest energy position and orientation in the bilayer, but the headgroup remains within its energetically accessible depth and angular ranges. Finally, the optimized docking geometry explains previous biophysical findings including mutations observed to disrupt membrane binding, and the rapid lateral diffusion observed for PIP3

  16. Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  17. Systematic variation of magnetic-field penetration depth in high-T(c) superconductors studied by muon spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.; Jacobson, A. J.; Lewandowski, J. T.; Brewer, J. H.; Kiefl, R. F.; Kreitzman, S. R.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 Sr0.15 CuO4 in transverse external magnetic fields 1 is approximately 4kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  18. Optimizations of spin-exchange relaxation-free magnetometer based on potassium and rubidium hybrid optical pumping

    SciTech Connect

    Fang, Jiancheng; Wang, Tao Li, Yang; Zhang, Hong; Zou, Sheng

    2014-12-15

    The hybrid optical pumping atomic magnetometers have not realized its theoretical sensitivity, the optimization is critical for optimal performance. The optimizations proposed in this paper are suitable for hybrid optical pumping atomic magnetometer, which contains two alkali species. To optimize the parameters, the dynamic equations of spin evolution with two alkali species were solved, whose steady-state solution is used to optimize the parameters. The demand of the power of the pump beam is large for hybrid optical pumping. Moreover, the sensitivity of the hybrid optical pumping magnetometer increases with the increase of the power density of the pump beam. The density ratio between the two alkali species is especially important for hybrid optical pumping magnetometer. A simple expression for optimizing the density ratio is proposed in this paper, which can help to determine the mole faction of the alkali atoms in fabricating the hybrid cell before the cell is sealed. The spin-exchange rate between the two alkali species is proportional to the saturated density of the alkali vapor, which is highly dependent on the temperature of the cell. Consequently, the sensitivity of the hybrid optical pumping magnetometer is dependent on the temperature of the cell. We proposed the thermal optimization of the hybrid cell for a hybrid optical pumping magnetometer, which can improve the sensitivity especially when the power of the pump beam is low. With these optimizations, a sensitivity of approximately 5 fT/Hz{sup 1/2} is achieved with gradiometer arrangement.

  19. Optimizations of spin-exchange relaxation-free magnetometer based on potassium and rubidium hybrid optical pumping.

    PubMed

    Fang, Jiancheng; Wang, Tao; Zhang, Hong; Li, Yang; Zou, Sheng

    2014-12-01

    The hybrid optical pumping atomic magnetometers have not realized its theoretical sensitivity, the optimization is critical for optimal performance. The optimizations proposed in this paper are suitable for hybrid optical pumping atomic magnetometer, which contains two alkali species. To optimize the parameters, the dynamic equations of spin evolution with two alkali species were solved, whose steady-state solution is used to optimize the parameters. The demand of the power of the pump beam is large for hybrid optical pumping. Moreover, the sensitivity of the hybrid optical pumping magnetometer increases with the increase of the power density of the pump beam. The density ratio between the two alkali species is especially important for hybrid optical pumping magnetometer. A simple expression for optimizing the density ratio is proposed in this paper, which can help to determine the mole faction of the alkali atoms in fabricating the hybrid cell before the cell is sealed. The spin-exchange rate between the two alkali species is proportional to the saturated density of the alkali vapor, which is highly dependent on the temperature of the cell. Consequently, the sensitivity of the hybrid optical pumping magnetometer is dependent on the temperature of the cell. We proposed the thermal optimization of the hybrid cell for a hybrid optical pumping magnetometer, which can improve the sensitivity especially when the power of the pump beam is low. With these optimizations, a sensitivity of approximately 5 fT/Hz(1/2) is achieved with gradiometer arrangement.

  20. Nuclear Spin Lattice Relaxation and Conductivity Studies of the Non-Arrhenius Conductivity Behavior in Lithium Fast Ion Conducting Sulfide Glasses

    SciTech Connect

    Benjamin Michael Meyer

    2003-05-31

    As time progresses, the world is using up more of the planet's natural resources. Without technological advances, the day will eventually arrive when these natural resources will no longer be sufficient to supply all of the energy needs. As a result, society is seeing a push for the development of alternative fuel sources such as wind power, solar power, fuel cells, and etc. These pursuits are even occurring in the state of Iowa with increasing social pressure to incorporate larger percentages of ethanol in gasoline. Consumers are increasingly demanding that energy sources be more powerful, more durable, and, ultimately, more cost efficient. Fast Ionic Conducting (FIC) glasses are a material that offers great potential for the development of new batteries and/or fuel cells to help inspire the energy density of battery power supplies. This dissertation probes the mechanisms by which ions conduct in these glasses. A variety of different experimental techniques give a better understanding of the interesting materials science taking place within these systems. This dissertation discusses Nuclear Magnetic Resonance (NMR) techniques performed on FIC glasses over the past few years. These NMR results have been complimented with other measurement techniques, primarily impedance spectroscopy, to develop models that describe the mechanisms by which ionic conduction takes place and the dependence of the ion dynamics on the local structure of the glass. The aim of these measurements was to probe the cause of a non-Arrhenius behavior of the conductivity which has been seen at high temperatures in the silver thio-borosilicate glasses. One aspect that will be addressed is if this behavior is unique to silver containing fast ion conducting glasses. more specifically, this study will determine if a non-Arrhenius correlation time, {tau}, can be observed in the Nuclear Spin Lattice Relaxation (NSLR) measurements. If so, then can this behavior be modeled with a new single distribution

  1. A general approach to the electronic spin relaxation of Gd(III) complexes in solutions. Monte Carlo simulations beyond the Redfield limit

    NASA Astrophysics Data System (ADS)

    Rast, S.; Fries, P. H.; Belorizky, E.; Borel, A.; Helm, L.; Merbach, A. E.

    2001-10-01

    The time correlation functions of the electronic spin components of a metal ion without orbital degeneracy in solution are computed. The approach is based on the numerical solution of the time-dependent Schrödinger equation for a stochastic perturbing Hamiltonian which is simulated by a Monte Carlo algorithm using discrete time steps. The perturbing Hamiltonian is quite general, including the superposition of both the static mean crystal field contribution in the molecular frame and the usual transient ligand field term. The Hamiltonian of the static crystal field can involve the terms of all orders, which are invariant under the local group of the average geometry of the complex. In the laboratory frame, the random rotation of the complex is the only source of modulation of this Hamiltonian, whereas an additional Ornstein-Uhlenbeck process is needed to describe the time fluctuations of the Hamiltonian of the transient crystal field. A numerical procedure for computing the electronic paramagnetic resonance (EPR) spectra is proposed and discussed. For the [Gd(H2O)8]3+ octa-aqua ion and the [Gd(DOTA)(H2O)]- complex [DOTA=1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclo dodecane] in water, the predictions of the Redfield relaxation theory are compared with those of the Monte Carlo approach. The Redfield approximation is shown to be accurate for all temperatures and for electronic resonance frequencies at and above X-band, justifying the previous interpretations of EPR spectra. At lower frequencies the transverse and longitudinal relaxation functions derived from the Redfield approximation display significantly faster decays than the corresponding simulated functions. The practical interest of this simulation approach is underlined.

  2. Molecular interactions in the ionic liquid emim acetate and water binary mixtures probed via NMR spin relaxation and exchange spectroscopy.

    PubMed

    Allen, Jesse J; Bowser, Sage R; Damodaran, Krishnan

    2014-05-01

    Interactions of ionic liquids (ILs) with water are of great interest for many potential IL applications. 1-Ethyl-3-methylimidazolium (emim) acetate, in particular, has shown interesting interactions with water including hydrogen bonding and even chemical exchange. Previous studies have shown the unusual behavior of emim acetate when in the presence of 0.43 mole fraction of water, and a combination of NMR techniques is used herein to investigate the emim acetate-water system and the unusual behavior at 0.43 mole fraction of water. NMR relaxometry techniques are used to describe the effects of water on the molecular motion and interactions of emim acetate with water. A discontinuity is seen in nuclear relaxation behavior at the concentration of 0.43 mole fraction of water, and this is attributed to the formation of a hydrogen bonded network. EXSY measurements are used to determine the exchange rates between the H2 emim proton and water, which show a complex dependence on the concentration of the mixture. The findings support and expand our previous results, which suggested the presence of an extended hydrogen bonding network in the emim acetate-water system at concentrations close to 0.50 mole fraction of H2O. PMID:24654003

  3. Effect of thermal annealing on electron spin relaxation of beryllium-doped In0.8Ga0.2As0.45P0.55 bulk

    NASA Astrophysics Data System (ADS)

    Wu, Hao; Ji, Lian; Harasawa, Ryo; Yasue, Yuya; Aritake, Takanori; Jiang, Canyu; Lu, Shulong; Tackeuchi, Atsushi

    2016-08-01

    The effect of thermal annealing on the electron spin relaxation of beryllium-doped In0.8Ga0.2As0.45P0.55 bulk was investigated by time-resolved spin-dependent pump and probe reflection measurement with a high time resolution of 200 fs. Three similar InGaAsP samples were examined one of which was annealed at 800 °C for 1 s, one was annealed at 700 °C for 1 s and the other was not annealed after crystal growth by molecular beam epitaxy. Although the carrier lifetimes of the 700 °C-annealed sample and the unannealed sample were similar, that of the 800 °C-annealed sample was extended to 11.6 (10.4) ns at 10 (300) K, which was more than two (four) times those of the other samples. However, interestingly the spin relaxation time of the 800 °C-annealed sample was found to be similar to those of the other two samples. Particularly at room temperature, the spin relaxation times are 143 ps, 147 ps, and 111 ps for the 800 °C-annealed sample, 700 °C-annealed sample, and the unannealed sample, respectively.

  4. Long-range Li+ dynamics in the lithium argyrodite Li7PSe6 as probed by rotating-frame spin-lattice relaxation NMR.

    PubMed

    Epp, V; Gün, O; Deiseroth, H-J; Wilkening, M

    2013-05-21

    Lithium-rich argyrodites belong to a relatively new group of fast ion conducting solids. They might serve as powerful electrolytes in all-solid-state lithium-ion batteries being, from a medium-term point of view, the key technology when safe energy storage systems have to be developed. Spin-lattice relaxation (SLR) nuclear magnetic resonance (NMR) measurements carried out in the rotating frame of reference turned out to be the method of choice to study Li dynamics in argyrodites. When plotted as a function of the inverse temperature, the SLR rates log10(R1ρ) reveal an asymmetric diffusion-induced rate peak. The rate peak contains information on the Li jump rate, the activation energy of the hopping process as well as correlation effects. In particular, considering the high-temperature flank of the SLR NMR rate peak recorded in the rotating frame of reference, an activation energy of approximately 0.49 eV is found. This value represents long-range lithium jump diffusion in crystalline Li7PSe6. As an example, at 325 K the Li jump rate determined from SLR NMR is in the order of 1.4 × 10(5) s(-1). The pronounced asymmetry of the rate peak R1ρ(1/T) points to correlated Li motion. It is comparable to that which is typically found for structurally disordered materials showing a broad range of correlation times.

  5. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results.

    PubMed

    Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas

    2015-08-01

    In a previous paper [Phys. Rev. E 83, 021801 (2011)] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ∼100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (μSR) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ∼100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the μSR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings. PMID:26382423

  6. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results

    NASA Astrophysics Data System (ADS)

    Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas

    2015-08-01

    In a previous paper [Phys. Rev. E 83, 021801 (2011), 10.1103/PhysRevE.83.021801] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ˜100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (μ SR ) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ˜100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the μ SR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.

  7. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results.

    PubMed

    Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas

    2015-08-01

    In a previous paper [Phys. Rev. E 83, 021801 (2011)] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ∼100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (μSR) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ∼100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the μSR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.

  8. Key role of spin-orbit effects in the relaxation of CO2(010) by thermal collisions with O(3Pj)

    NASA Astrophysics Data System (ADS)

    de Lara-Castells, M. P.; Hernández, Marta I.; Delgado-Barrio, G.; Villarreal, P.; López-Puertas, M.

    The quenching of CO2(010) by thermal collisions with ground-state atomic oxygen is a crucial process in determining the cooling rates of the thermospheres of Earth, Venus and Mars and then to predict changes due to the increase of this green-house gas. One of the questions raised by the experiments and aeronomical observations is with regard to the physical origin of the non-Landau-Teller and negligible temperature dependence of the vibrational relaxation rate at the temperatures existing in the thermospheres (150K≤T≥550 K). In this context, we extend our previous work on quantum scattering calculations performed on high-quality ab initio potential energy surfaces (PESs) [M. P. de Lara-Castells, Marta I. Hernández, G. Delgado-Barrio, P. Villarreal, and M. López-Puertas, J. Chem. Phys. 124, 164302 (2006)]. and report translational-energy averaged quenching probabilities for the previously reported C2v PES as well as for additional orientational approaches of the oxygen atom. Our results reveal the spin-orbit couplings to be responsible for the temperature dependence of the quenching rate estimated from the analysis of upper atmospheric data. In addition, we analyse the effect of the PESs' anisotropy on the quenching process.

  9. Quantum criticality in single crystalline YFe2 Al10 determined from zero-field and longitudinal-field muon spin relaxation

    NASA Astrophysics Data System (ADS)

    Huang, Kevin; Tan, Cheng; Zhang, Jian; Ding, Zhaofeng; Maclaughlin, Douglas; Bernal, Oscar; Ho, Pei-Chun; Wu, Liusuo; Aronson, Meigan; Shu, Lei

    Muon spin relaxation (μSR) measurements were performed on single crystalline YFe2Al10 down to 19 mK and in magnetic fields up to ~100 Oe. Zero-field- μSR measurements showed no evidence of magnetic order down to 19 mK, consistent with previous measurements. However, we also find that the depolarization rate Λ is temperature independent above 1 K but increases in an exponential behavior for T < 1 K. Longitudinal-field μSR measurements also reveals a time-field scaling where G (t , H) = G (t /Hγ), with γ = 0.67. This is further confirmed from the magnetic field dependence of Λ, which finds Λ (H) ~H0. 67 at 19 mK. This is further evidence that single crystalline YFe2Al10 is in close proximity to a ferromagnetic quantum critical point. The research performed in this study was supported by the National NSF of China under Grant No. 11474060 and STCSM of China (No. 15XD1500200). Work at CSULA funded by NSF/DMR-1105380. Research at CSU-Fresno is supported by NSF DMR-1506677.

  10. Ion hopping in crystalline and glassy spodumene LiAl Si2 O6 : 7Li spin-lattice relaxation and 7Li echo NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Qi, F.; Rier, C.; Böhmer, R.; Franke, W.; Heitjans, P.

    2005-09-01

    Nuclear magnetic resonance spectroscopy was used to study polycrystalline β -spodumene (β-LiAlSi2O6) as well as glassy specimens with the same chemical composition. Li7 spin-lattice relaxation measurements were carried out in a broad temperature range and for several Larmor frequencies. In addition to a pronounced rate maximum at high temperatures, stemming from the long-range Li motion in these aluminosilicates, we found a weak maximum in the crystalline modification near 120K . The latter result confirms the existence of a local double-well structure in which the Li ions reside. The ionic motion was also monitored by solid- and stimulated-echo spectra as well as by the decay of the Jeener-Broekaert echo. Under conditions which are discussed in detail, the latter is a direct measure of the hopping correlation function. For the glass this function was found to decay faster and more stretched than that of the crystal at a given temperature. Furthermore, the relevant barriers against the high-temperature long-range Li motion are larger in the crystal as compared to the glass.

  11. Using multiple quantum coherence to increase the 15N resolution in a three-dimensional TROSY HNCO experiment for accurate PRE and RDC measurements.

    PubMed

    Hu, Kaifeng; Doucleff, Michaeleen; Clore, G Marius

    2009-10-01

    We present a new version of the 3D TROSY HNCO pulse scheme, referred to as HR-TROSY HNCO, with comparable resolution in the (15)N dimension to a 2D (1)H-(15)N HSQC experiment. In the conventional 3D TROSY HNCO, the constant time period (1/2J(NC) approximately 32 ms) severely limits the maximum resolution in the (15)N dimension. In the HR-TROSY HNCO experiment presented here, both constant time periods (approximately 32 ms each) for coherence forward and backward transfer between (15)N and (13)C' are utilized to double the (15)N evolution time. This leads to a dramatic enhancement in peak separation along the (15)N dimension, making the HR-TROSY HNCO an ideal pulse scheme for accurate paramagnetic relaxation enhancement and residual dipolar coupling measurements. PMID:19615926

  12. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    SciTech Connect

    S. -H. Baek; Gu, G. D.; Utz, Y.; Hucker, M.; Buchner, B.; Grafe, H. -J.

    2015-10-26

    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for large fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.

  13. Flexibility at a glycosidic linkage revealed by molecular dynamics, stochastic modeling, and (13)C NMR spin relaxation: conformational preferences of α-L-Rhap-α-(1 → 2)-α-L-Rhap-OMe in water and dimethyl sulfoxide solutions.

    PubMed

    Pendrill, Robert; Engström, Olof; Volpato, Andrea; Zerbetto, Mirco; Polimeno, Antonino; Widmalm, Göran

    2016-01-28

    The monosaccharide L-rhamnose is common in bacterial polysaccharides and the disaccharide α-L-Rhap-α-(1 → 2)-α-L-Rhap-OMe represents a structural model for a part of Shigella flexneri O-antigen polysaccharides. Utilization of [1'-(13)C]-site-specific labeling in the anomeric position at the glycosidic linkage between the two sugar residues facilitated the determination of transglycosidic NMR (3)JCH and (3)JCC coupling constants. Based on these spin-spin couplings the major state and the conformational distribution could be determined with respect to the ψ torsion angle, which changed between water and dimethyl sulfoxide (DMSO) as solvents, a finding mirrored by molecular dynamics (MD) simulations with explicit solvent molecules. The (13)C NMR spin relaxation parameters T1, T2, and heteronuclear NOE of the probe were measured for the disaccharide in DMSO-d6 at two magnetic field strengths, with standard deviations ≤1%. The combination of MD simulation and a stochastic description based on the diffusive chain model resulted in excellent agreement between calculated and experimentally observed (13)C relaxation parameters, with an average error of <2%. The coupling between the global reorientation of the molecule and the local motion of the spin probe is deemed essential if reproduction of NMR relaxation parameters should succeed, since decoupling of the two modes of motion results in significantly worse agreement. Calculation of (13)C relaxation parameters based on the correlation functions obtained directly from the MD simulation of the solute molecule in DMSO as solvent showed satisfactory agreement with errors on the order of 10% or less. PMID:26741055

  14. Linewidth narrowing in the epr spectra of Gd 3+ impurity ions due to the spin-lattice relaxation of lanthanide Kramers' host ions

    NASA Astrophysics Data System (ADS)

    Malhotra, V. M.; Dixon, J. M.; Buckmaster, H. A.

    1980-08-01

    Electron paramagnetic resonance (EPR) of Gd 3+ doped in some lanthanide Kramers' host ion single crytals of the sulfate octahydrates (Ln 2(SO 4) 3·8H 2O;Ln≡Nd,Sm,Dy and Er) and trichloride hexahydrates (LnCl 3·6H 2O;Ln≡Nd, Sm, Dy, Er and Yb) has been studied at T ≅ 297 K using a 9.4 GHz EPR spectrometer. The effect of the Kramers' host Ln 3+ ions on the g-values and linewidths of Gd 3+ spectra has been determined by comparison with those for the isostructural diamagnetic La, Y lattices. At 297 K,in the EPR transitions of Gd 3+ ions have narrow linewidths in spite of the presence of paramagnetic host ions like Nd 3+, Sm 3+ and Yb 3+, whereas an unusual variation in the linewidth is observed in the Dy 3+, Er 3+ hosts as well as a negative g-value shift. In these latter hosts, the linewidths of the Δ M = ± 1 transitions decrease progressively as the magnitude of M increases. The observation of resolved Gd 3+ spectra at 297 K in the above hosts has been interpreted in terms of a random modulation of the interactions between the Gd 3+ and the host Ln 3+ ions by the rapid spin-lattice relaxation of Ln 3+ ions following the generalized theory of magnetic resonance by Kubo and Tomita [15]. τ 1 for Ln 3+ has been estimated in the above mentioned Kramers' hosts from the observed EPR linewidths of Gd 3+ spectra. Values for τ 1 have also been computed for Ln 3+ ions in Ln(C 2H 5SO 4) 3. 9H 2O and LnF 3 from linewidth data in the literature. The results are consistent with an effective host spin-lattice time which is due to Orbach and/or Raman processes, depending upon the temperature and the ground state energy level scheme.

  15. Muon spin relaxation study on itinerant ferromagnet CeCrGe₃ and the effect of Ti substitution on magnetism of CeCrGe₃.

    PubMed

    Das, Debarchan; Bhattacharyya, A; Anand, V K; Hillier, A D; Taylor, J W; Gruner, T; Geibel, C; Adroja, D T; Hossain, Z

    2015-01-14

    A Muon spin relaxation (µSR) study has been performed on the Kondo lattice heavy fermion itinerant ferromagnet CeCrGe3. Recent investigations of bulk properties have revealed a long-range ordering of Cr moments at Tc = 70 K in this compound. Our µSR investigation between 1.2 K and 125 K confirm the bulk magnetic order which is marked by a loss in initial asymmetry below 70 K accompanied with a sharp increase in the muon depolarization rate. Field dependent µSR spectra show that the internal field at the muon site is higher than 0.25 T apparently due to the ferromagnetic nature of ordering. The effect of Ti substitution on the magnetism in CeCrGe3 is presented. A systematic study has been made on polycrystalline CeCr(1-x)Ti(x)Ge3 (0 ⩽ x ⩽ 1) using magnetic susceptibility χ(T), isothermal magnetization M(H), specific heat C(T) and electrical resistivity ρ(T) measurements which clearly reveal that the substitution of Ti for Cr in CeCrGe3 strongly influences the exchange interaction and ferromagnetic ordering of Cr moments. The Cr moment ordering temperature is suppressed gradually with increasing Ti concentration up to x = 0.50 showing Tc = 7 K beyond which Ce moment ordering starts to dominate and a crossover between Cr and Ce moment ordering is observed with a Ce moment ordering Tc = 14 K for x = 1.0. The Kondo lattice behavior is evident from temperature dependence of ρ(T) in all CeCr(1-x)Ti(x)Ge3 samples.

  16. 13C-NMR off-resonance rotating frame spin-lattice relaxation studies of bovine lens gamma-crystallin self association: effect of 'macromolecular crowding'.

    PubMed

    Stevens, A; Wang, S X; Caines, G H; Schleich, T

    1995-01-01

    The NMR technique of 13C off-resonance rotating frame spin-lattice relaxation, which provides an accurate assessment of the effective rotational correlation time (tau 0, eff) for macromolecular rotational diffusion, was applied to the study of gamma-crystallin association as a function of protein concentration and temperature. Values of the effective rotational correlation time for gamma-crystallin rotational diffusion were obtained at moderate to high protein concentrations (80-350 mg/ml) and at temperatures above, and below, the cold cataract phase transition temperature. With increasing concentration gamma-crystallin was observed to increasingly associate as reflected by larger values of tau 0, eff Decreasing temperature in the range of 35 to 22 degrees C was found to result in no change in the temperature corrected value of tau 0, eff at a gamma-crystallin concentration of 80 mg/ml, whereas at temperatures of 18 degrees C or below, this parameter was approx. twofold larger, suggesting the occurrence of a well defined phase transition, which correlated well with the cold cataract phase transition temperature. At higher protein concentrations, by contrast, tau 0, eff (temperature corrected) was found to increase by approx. 1.6- to 2-times in the temperature interval 35 degrees C to 22 degrees C, a result consistent with the dependence of the cold cataract phase transition temperature on gamma-crystallin concentration. Analysis of intensity ratio dispersion curves, using an assumed model of isodesmic association, permitted the estimation of the association constant characterizing the aggregation under particular conditions of concentration and temperature. The significant increase in the value of the association constant with moderate increases in protein concentration was rationalized by invoking the effect of 'macromolecular crowding'. The results obtained in this study suggest that in the intact lens, where high protein concentrations prevail, gamma

  17. Synthesis of 2,5-bis(spirocyclohexane)-substituted nitroxides of pyrroline and pyrrolidine series, including thiol-specific spin label: an analogue of MTSSL with long relaxation time.

    PubMed

    Kirilyuk, Igor A; Polienko, Yuliya F; Krumkacheva, Olesya A; Strizhakov, Rodion K; Gatilov, Yurii V; Grigor'ev, Igor A; Bagryanskaya, Elena G

    2012-09-21

    The nitroxides of 7-azadispiro[5.1.5.2]pentadecane and 7-azadispiro[5.1.5.2]pentadeca-14-ene series have been prepared, including thiol-specific methane thiosulfonate spin label for site-directed spin labeling. The effect of spirocyclohexane moieties on chemical and spectral properties has been studied. The obtained temperature dependencies of electron spin relaxation parameters demonstrate that new nitroxides may be suitable for PELDOR distance measurements at 80-120 K. Moreover, the new nitroxides demonstrated much higher stability toward reduction by ascorbate than spirocyclohexane-substituted nitroxides of piperidine series and showed 1.3-3.14 times lower reduction rates compared to corresponding 2,2,5,5-tetramethyl nitroxides. PMID:22917445

  18. (15)N Heteronuclear Chemical Exchange Saturation Transfer MRI.

    PubMed

    Zeng, Haifeng; Xu, Jiadi; Yadav, Nirbhay N; McMahon, Michael T; Harden, Bradley; Frueh, Dominique; van Zijl, Peter C M

    2016-09-01

    A two-step heteronuclear enhancement approach was combined with chemical exchange saturation transfer (CEST) to magnify (15)N MRI signal of molecules through indirect detection via water protons. Previous CEST studies have been limited to radiofrequency (rf) saturation transfer or excitation transfer employing protons. Here, the signal of (15)N is detected indirectly through the water signal by first inverting selectively protons that are scalar-coupled to (15)N in the urea molecule, followed by chemical exchange of the amide proton to bulk water. In addition to providing a small sensitivity enhancement, this approach can be used to monitor the exchange rates and thus the pH sensitivity of the participating (15)N-bound protons. PMID:27548755

  19. Relaxation times of spin states of all ranks and orders of quadrupolar nuclei estimated from NMR z-spectra: Markov chain Monte Carlo analysis applied to 7Li+ and 23Na+ in stretched hydrogels.

    PubMed

    Kuchel, Philip W; Naumann, Christoph; Puckeridge, Max; Chapman, Bogdan E; Szekely, David

    2011-09-01

    The NMR z-spectra of 7Li+ and 23Na+ in stretched hydrogels contain five minima, or critical values, with a sharp "dagger" on the central dip. The mathematical representation of such z-spectra from spin-3/2 nuclei contains nine distinct (the total is 15 but there is redundancy of the ±order-numbers) relaxation rate constants that are unique for each of the spin states, up to rank 3, order 3. We present an approach to multiple-parameter-value estimation that exploits the high level of separability of the effects of each of the relaxation rate constants on the features of the z-spectrum. The Markov chain Monte Carlo (MCMC) method is computationally demanding but it yielded statistically robust estimates (low coefficients of variation) of the parameter values. We describe the implementation of the MCMC analysis (in the present context) and posit that it can obviate the need for using multiple-quantum filtered RF-pulse sequences to estimate all relaxation rate constants/times under experimentally favorable, but readily achievable, circumstances.

  20. Investigation of electron relaxation in the metal proteins containing the single paramagnetic centers of integer spin by nuclear forward scattering of synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Popov, E. A.; Yanvarev, Eugene A.; Bashkirov, Sh. S.; Kouznetsov, V. I.

    2001-11-01

    Nuclear forward scattering (NFS) of synchrotron radiation (SR) is being modeled in metal proteins containing the single paramagnetic centers of integer spin (Fe2+). It is known the spin fluctuations in the electron environment of Moessbauer ion Fe2+ will be manifested itself in NFS if a sample undergoes the influence of applied magnetic field of a few Tesla. Under the condition we are analyzing how the resonant response (RR) of a sample to SR pulse will be changed due to the both spin-lattice and spin-spin interactions.

  1. Phenylalanine δ15N in Paleo Archives as a New Proxy for δ15N of Exported Primary Production

    NASA Astrophysics Data System (ADS)

    McCarthy, M.; Batista, F. C.; Vokhshoori, N. L.; Brown, J. T.; Guilderson, T. P.; Ravelo, A. C.; Sherwood, O.

    2012-12-01

    Compound-specific isotope analysis of individual amino acids (CSI-AA) is emerging as a powerful new tool for studying the paleo nitrogen cycle. Because most detrital organic nitrogen is composed of amino acids, CSI-AA can reveal the mechanistic basis for organic nitrogen diagenesis, preserve a record of past food web structure, and potentially reconstruct the δ15N values of past nitrate and primary production. Within the commonly measured amino acids, the δ15N value of phenylalanine (Phe) appears uniquely promising as a new proxy that reflects the nitrogen isotopic value of the original source. Phe δ15N values remain almost unchanged with trophic transfer through food webs, and also during at least the initial stages of organic matter degradation. Here we synthesize results from both bio-archives and recent sediments, which together suggest that at least in Holocene archives the Phe δ15N value does in fact record the average inorganic nitrogen δ15N value at the base of planktonic food webs. However, several important unknowns also remain. These include the extent of variation in amino acid isotopic fractionation patterns in phylogenetically distinct algal groups. The stability of Phe δ15N values in older sediments where organic matter has undergone extensive diagenesis is also an important research area, which may ultimately establish the temporal limit for application of this approach to study past geological epochs. Together, however, results to date suggest that of Phe δ15N values in paleo archives represent a novel molecular-level proxy which is not tied to any specific organism or group, but rather can provide an integrated estimate of δ15N value of exported primary production.

  2. Fast Li ion dynamics in the solid electrolyte Li7 P3 S11 as probed by (6,7) Li NMR spin-lattice relaxation.

    PubMed

    Wohlmuth, Dominik; Epp, Viktor; Wilkening, Martin

    2015-08-24

    The development of safe and long-lasting all-solid-state batteries with high energy density requires a thorough characterization of ion dynamics in solid electrolytes. Commonly, conductivity spectroscopy is used to study ion transport; much less frequently, however, atomic-scale methods such as nuclear magnetic resonance (NMR) are employed. Here, we studied long-range as well as short-range Li ion dynamics in the glass-ceramic Li7 P3 S11 . Li(+) diffusivity was probed by using a combination of different NMR techniques; the results are compared with those obtained from electrical conductivity measurements. Our NMR relaxometry data clearly reveal a very high Li(+) diffusivity, which is reflected in a so-called diffusion-induced (6) Li NMR spin-lattice relaxation peak showing up at temperatures as low as 313 K. At this temperature, the mean residence time between two successful Li jumps is in the order of 3×10(8) s(-1) , which corresponds to a Li(+) ion conductivity in the order of 10(-4) to 10(-3) S cm(-1) . Such a value is in perfect agreement with expectations for the crystalline but metastable glass ceramic Li7 P3 S11 . In contrast to conductivity measurements, NMR analysis reveals a range of activation energies with values ranging from 0.17 to 0.26 eV, characterizing Li diffusivity in the bulk. In our case, through-going Li ion transport, when probed by using macroscopic conductivity spectroscopy, however, seems to be influenced by blocking grain boundaries including, for example, amorphous regions surrounding the Li7 P3 S11 crystallites. As a result of this, long-range ion transport as seen by impedance spectroscopy is governed by an activation energy of approximately 0.38 eV. The findings emphasize how surface and grain boundary effects can drastically affect long-range ionic conduction. If we are to succeed in solid-state battery technology, such effects have to be brought under control by, for example, sophisticated densification or through the preparation

  3. Evolution of Slow Magnetic Relaxation: from Diamagnetic Matrix Y(OH)CO3 to Dy(0.06)Y(0.94)(OH)CO3 with High Spin-Reversal Barrier and Blocking Temperature.

    PubMed

    Liu, Jiang; Chen, Yan-Cong; Lai, Jia-Jun; Wu, Zi-Hao; Wang, Long-Fei; Li, Quan-Wen; Huang, Guo-Zhang; Jia, Jian-Hua; Tong, Ming-Liang

    2016-03-21

    A stable Dy(III)-dispersed compound with single-molecule magnet behavior, Dy(0.06)Y(0.94)(OH)CO3, was isolated by a general strategy targeted at the doping of paramagnetic Dy(3+) into a diamagnetic 3D inorganic network of Y(OH)CO3. The single-ion origin of slow magnetic relaxation was gradually released as variations of the dysprosium/yttrium ratio and finally gave a relatively large spin-reversal barrier around 200 K and high hysteresis temperature of 8 K. This study opens up new opportunities to investigate the slow magnetic relaxation and magnetostructural correlation by choosing a suitable inorganic architecture with strong axial anisotropy. PMID:26959174

  4. Non-Arrhenius conductivity in the fast ionic conductor Li{sub 0.5}La{sub 0.5}TiO{sub 3}: Reconciling spin-lattice and electrical-conductivity relaxations

    SciTech Connect

    Leon, C.; Santamaria, J.; Ibarra, J.; Torres, L.M.

    1997-09-01

    Nuclear magnetic resonance and electrical conductivity measurements are conducted to study the dynamics of the ionic diffusion process in the crystalline ionic conductor Li{sub 0.5}La{sub 0.5}TiO{sub 3}. dc conductivity shows a non-Arrhenius temperature dependence, similar to the one recently reported for some ionic conducting glasses. Spin-lattice and conductivity relaxations are analyzed in the same frequency and temperature range in terms of the non-Arrhenius dependence of the correlation time. Both relaxations are then described using a single correlation function of the form f(t)=exp{bold (}{minus}(t/{tau}){sup {beta}}{bold )}, with {beta}=0.4 over the whole temperature range. {copyright} {ital 1997} {ital The American Physical Society}

  5. The time correlation function perspective of NMR relaxation in proteins

    NASA Astrophysics Data System (ADS)

    Shapiro, Yury E.; Meirovitch, Eva

    2013-08-01

    We applied over a decade ago the two-body coupled-rotator slowly relaxing local structure (SRLS) approach to NMR relaxation in proteins. One rotator is the globally moving protein and the other rotator is the locally moving probe (spin-bearing moiety, typically the 15N-1H bond). So far we applied SRLS to 15N-H relaxation from seven different proteins within the scope of the commonly used data-fitting paradigm. Here, we solve the SRLS Smoluchowski equation using typical best-fit parameters as input, to obtain the corresponding generic time correlation functions (TCFs). The following new information is obtained. For actual rhombic local ordering and main ordering axis pointing along C_{i - 1}^α - C_i^α, the measurable TCF is dominated by the (K,K') = (-2,2), (2,2), and (0,2) components (K is the order of the rank 2 local ordering tensor), determined largely by the local motion. Global diffusion axiality affects the analysis significantly when the ratio between the parallel and perpendicular components exceeds approximately 1.5. Local diffusion axiality has a large and intricate effect on the analysis. Mode-coupling becomes important when the ratio between the global and local motional rates falls below 0.01. The traditional method of analysis - model-free (MF) - represents a simple limit of SRLS. The conditions under which the MF and SRLS TCFs are the same are specified. The validity ranges of wobble-in-a-cone and rotation on the surface of a cone as local motions are determined. The evolution of the intricate Smoluchowski operator from the simple diffusion operator for a sphere reorienting in isotropic medium is delineated. This highlights the fact that SRLS is an extension of the established stochastic theories for treating restricted motions. This study lays the groundwork for TCF-based comparison between mesoscopic SRLS and atomistic molecular dynamics.

  6. Effects of spin-lock field direction on the quantitative measurement of spin-lattice relaxation time constant in the rotating frame (T1ρ) in a clinical MRI system

    SciTech Connect

    Yee, Seonghwan; Gao, Jia-Hong

    2014-12-15

    Purpose: To investigate whether the direction of spin-lock field, either parallel or antiparallel to the rotating magnetization, has any effect on the spin-lock MRI signal and further on the quantitative measurement of T1ρ, in a clinical 3 T MRI system. Methods: The effects of inverted spin-lock field direction were investigated by acquiring a series of spin-lock MRI signals for an American College of Radiology MRI phantom, while the spin-lock field direction was switched between the parallel and antiparallel directions. The acquisition was performed for different spin-locking methods (i.e., for the single- and dual-field spin-locking methods) and for different levels of clinically feasible spin-lock field strength, ranging from 100 to 500 Hz, while the spin-lock duration was varied in the range from 0 to 100 ms. Results: When the spin-lock field was inverted into the antiparallel direction, the rate of MRI signal decay was altered and the T1ρ value, when compared to the value for the parallel field, was clearly different. Different degrees of such direction-dependency were observed for different spin-lock field strengths. In addition, the dependency was much smaller when the parallel and the antiparallel fields are mixed together in the dual-field method. Conclusions: The spin-lock field direction could impact the MRI signal and further the T1ρ measurement in a clinical MRI system.

  7. Refining cotton-wick method for 15N plant labelling.

    NASA Astrophysics Data System (ADS)

    Fustec, Joëlle; Mahieu, Stéphanie

    2010-05-01

    The symbiosis Fabaceae/Rhizobiaceae plays a critical role in the nitrogen cycle. It gives the plant the ability to fix high amounts of atmospheric N. A part of this N can be transferred to the soil via rhizodeposition. The contribution of Fabaceae to the soil N pool is difficult to measure, since it is necessary for assessing N benefits for other crops, for soil biological activity, and for reducing water pollution in sustainable agriculture (Fustec, 2009). The aim of this study was to test and improve the reliability of the 15N cotton-wick method for measuring the soil N derived from plant rhizodeposition (Mahieu et al., 2007). The effects of the concentration of the 15N-urea labelling solution and of the feeding frequency (continuous or pulses) on the assessment of nitrogen rhizodeposition were studied in two greenhouse experiments using the field pea (Pisum sativum L.) and the non-nodulating isoline P2. The plant parts and the soil were prepared for 15N:14N measurements for assessing N rhizodeposition (Mahieu et al., 2009). The fraction of plants' belowground nitrogen allocated to rhizodeposition in both Frisson pea and P2 was 20 to more than 50% higher when plants were labelled continuously than when they were labelled using fortnightly pulses. Our results suggested that when 15N root enrichment was high, nitrogen rhizodeposition was underestimated only for plants that were 15N-fed by fortnightly pulses, and not in plants 15N-fed continuously. This phenomenon was especially observed for plants relying on symbiotic N fixation for N acquisition; it may be linked to the concentration of the labelling solution. In conclusion, N rhizodeposition assessment was strongly influenced by the 15N-feeding frequency and the concentration of the labelling solution. The estimation of N rhizodeposition was more reliable when plants were labelled continuously with a dilute solution of 15N urea. Fustec et al. 2009. Agron. Sustain. Dev., DOI 10.1051/agro/2009003, in press. Mahieu

  8. Biosynthetic uniform 13C,15N-labelling of zervamicin IIB. Complete 13C and 15N NMR assignment.

    PubMed

    Ovchinnikova, Tatyana V; Shenkarev, Zakhar O; Yakimenko, Zoya A; Svishcheva, Natalia V; Tagaev, Andrey A; Skladnev, Dmitry A; Arseniev, Alexander S

    2003-01-01

    Zervamicin IIB is a member of the alpha-aminoisobutyric acid containing peptaibol antibiotics. A new procedure for the biosynthetic preparation of the uniformly 13C- and 15N-enriched peptaibol is described This compound was isolated from the biomass of the fungus-producer Emericellopsis salmosynnemata strain 336 IMI 58330 obtained upon cultivation in the totally 13C, 15N-labelled complete medium. To prepare such a medium the autolysed biomass and the exopolysaccharides of the obligate methylotrophic bacterium Methylobacillus flagellatus KT were used. This microorganism was grown in totally 13C, 15N-labelled minimal medium containing 13C-methanol and 15N-ammonium chloride as the only carbon and nitrogen sources. Preliminary NMR spectroscopic analysis indicated a high extent of isotope incorporation (> 90%) and led to the complete 13C- and 15N-NMR assignment including the stereospecific assignment of Aib residues methyl groups. The observed pattern of the structurally important secondary chemical shifts of 1H(alpha), 13C=O and 13C(alpha) agrees well with the previously determined structure of zervamicin IIB in methanol solution. PMID:14658801

  9. Relaxation selective pulses in fast relaxing systems.

    PubMed

    Lopez, Christopher J; Lu, Wei; Walls, Jamie D

    2014-05-01

    In this work, the selectivity or sharpness of the saturation profiles for relaxation selective pulses (R^rsps) that suppress magnetization possessing relaxation times of T2=T2(rsp) and T1=αT2 for α∈12,∞ was optimized. Along with sharpening the selectivity of the R^rsps, the selective saturation of these pulses was also optimized to be robust to both B0 and B1 inhomogeneities. Frequency-swept hyperbolic secant and adiabatic time-optimal saturation pulse inputs were found to work best in the optimizations, and the pulse lengths required to selectivity saturate the magnetization were always found to be less than the inversion recovery delay, T1ln(2). The selectivity of the optimized relaxation selective pulses was experimentally demonstrated in aqueous solutions with varying concentrations of the paramagnetic species, [Mn(+2)], and for use in solvent suppression. Finally, the "rotational" properties of spin relaxation were explored along with an analytical derivation of adiabatic time-optimal saturation pulses. PMID:24631803

  10. Solid state {sup 1}H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: The relationship between structure and methyl group and t-butyl group rotation

    SciTech Connect

    Wang, Xianlong E-mail: pbeckman@brynmawr.edu; Mallory, Frank B.; Mallory, Clelia W.; Odhner, Hosanna R.; Beckmann, Peter A. E-mail: pbeckman@brynmawr.edu

    2014-05-21

    We report ab initio density functional theory electronic structure calculations of rotational barriers for t-butyl groups and their constituent methyl groups both in the isolated molecules and in central molecules in clusters built from the X-ray structure in four t-butyl aromatic compounds. The X-ray structures have been reported previously. We also report and interpret the temperature dependence of the solid state {sup 1}H nuclear magnetic resonance spin-lattice relaxation rate at 8.50, 22.5, and 53.0 MHz in one of the four compounds. Such experiments for the other three have been reported previously. We compare the computed barriers for methyl group and t-butyl group rotation in a central target molecule in the cluster with the activation energies determined from fitting the {sup 1}H NMR spin-lattice relaxation data. We formulate a dynamical model for the superposition of t-butyl group rotation and the rotation of the t-butyl group's constituent methyl groups. The four compounds are 2,7-di-t-butylpyrene, 1,4-di-t-butylbenzene, 2,6-di-t-butylnaphthalene, and 3-t-butylchrysene. We comment on the unusual ground state orientation of the t-butyl groups in the crystal of the pyrene and we comment on the unusually high rotational barrier of these t-butyl groups.

  11. Effect of H bond removal and changes in the position of the iron-sulphur head domain on the spin-lattice relaxation properties of the [2Fe-2S](2+) Rieske cluster in cytochrome bc(1).

    PubMed

    Sarewicz, Marcin; Dutka, Małgorzata; Pietras, Rafał; Borek, Arkadiusz; Osyczka, Artur

    2015-10-14

    Here, comparative electron spin-lattice relaxation studies of the 2Fe-2S iron-sulphur (Fe-S) cluster embedded in a large membrane protein complex - cytochrome bc1 - are reported. Structural modifications of the local environment alone (mutations S158A and Y160W removing specific H bonds between Fe-S and amino acid side chains) or in combination with changes in global protein conformation (mutations/inhibitors changing the position of the Fe-S binding domain within the protein complex) resulted in different redox potentials as well as g-, g-strain and the relaxation rates (T1(-1)) for the Fe-S cluster. The relaxation rates for T < 25 K were measured directly by inversion recovery, while for T > 60 K they were deduced from simulation of continuous wave EPR spectra of the cluster using a model that included anisotropy of Lorentzian broadening. In all cases, the relaxation rate involved contributions from direct, second-order Raman and Orbach processes, each dominating over different temperature ranges. The analysis of T1(-1) (T) over the range 5-120 K yielded the values of the Orbach energy (EOrb), Debye temperature θD and Raman process efficiency CRam for each variant of the protein. As the Orbach energy was generally higher for mutants S158A and Y160W, compared to wild-type protein (WT), it is suggested that H bond removal influences the geometry leading to increased strength of antiferromagnetic coupling between two Fe ions of the cluster. While θD was similar for all variants (∼107 K), the efficiency of the Raman process generally depends on the spin-orbit coupling that is lower for S158A and Y160W mutants, when compared to the WT. However, in several cases CRam did not only correlate with spin-orbit coupling but was also influenced by other factors - possibly the modification of protein rigidity and therefore the vibrational modes around the Fe-S cluster that change upon the movement of the iron-sulphur head domain.

  12. Strategy for the study of paramagnetic proteins with slow electronic relaxation rates by nmr spectroscopy: application to oxidized human [2Fe-2S] ferredoxin.

    PubMed

    Machonkin, Timothy E; Westler, William M; Markley, John L

    2004-05-01

    NMR studies of paramagnetic proteins are hampered by the rapid relaxation of nuclei near the paramagnetic center, which prevents the application of conventional methods to investigations of the most interesting regions of such molecules. This problem is particularly acute in systems with slow electronic relaxation rates. We present a strategy that can be used with a protein with slow electronic relaxation to identify and assign resonances from nuclei near the paramagnetic center. Oxidized human [2Fe-2S] ferredoxin (adrenodoxin) was used to test the approach. The strategy involves six steps: (1) NMR signals from (1)H, (13)C, and (15)N nuclei unaffected or minimally affected by paramagnetic effects are assigned by standard multinuclear two- and three-dimensional (2D and 3D) spectroscopic methods with protein samples labeled uniformly with (13)C and (15)N. (2) The very broad, hyperfine-shifted signals from carbons in the residues that ligate the metal center are classified by amino acid and atom type by selective (13)C labeling and one-dimensional (1D) (13)C NMR spectroscopy. (3) Spin systems involving carbons near the paramagnetic center that are broadened but not hyperfine-shifted are elucidated by (13)C[(13)C] constant time correlation spectroscopy (CT-COSY). (4) Signals from amide nitrogens affected by the paramagnetic center are assigned to amino acid type by selective (15)N labeling and 1D (15)N NMR spectroscopy. (5) Sequence-specific assignments of these carbon and nitrogen signals are determined by 1D (13)C[(15)N] difference decoupling experiments. (6) Signals from (1)H nuclei in these spin systems are assigned by paramagnetic-optimized 2D and 3D (1)H[(13)C] experiments. For oxidized human ferredoxin, this strategy led to assignments (to amino acid and atom type) for 88% of the carbons in the [2Fe-2S] cluster-binding loops (residues 43-58 and 89-94). These included complete carbon spin-system assignments for eight of the 22 residues and partial assignments for

  13. Stepwise enrichment of 15N along food chains: Further evidence and the relation between δ 15N and animal age

    NASA Astrophysics Data System (ADS)

    Minagawa, Masao; Wada, Eitaro

    1984-05-01

    The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone. Primary producers, showed average δ15Nversus atmospheric nitrogen of +5.0%. (+3.4 to +7.5) in the Bering Sea and Lake Ashinoko, and +6.8%. (+6.0 to +7.6) in Usujiri intertidal zone. Blue green algae from the East China Sea show an average -0.55%. (-0.8 to +1.2). All consumers, Zooplankton, fish and bird exhibited Stepwise enrichment of 15N with increasing trophic level. The 15N enrichment at a single feeding process ranged from +1.3 to +5.3 averaging +3.4 ± 1.1%.. This isotopic fractionation seems to be independent of habitat. The effect of age in animals was obtained by analyzing two marine mussels. The soft tissue nitrogen showed +2.0%. enrichment relative to that of primary producers, and the magnitude was almost constant with shell ages ranging from 0 to 8 years. A similar 15N enrichment occurs in all Molluscs, Crustaceans, Insecta, Amphibia, Fish, Ave and Mammal species regardless of the difference in the form of excreted nitrogen and in laboratory cultured fish, brine shrimp and mice (+2.9 to +4.9%.). The excreted ammonia from guppy was sufficiently light to balance the concentration of 15N to animal body.

  14. Natural abundance (14)N and (15)N solid-state NMR of pharmaceuticals and their polymorphs.

    PubMed

    Veinberg, Stanislav L; Johnston, Karen E; Jaroszewicz, Michael J; Kispal, Brianna M; Mireault, Christopher R; Kobayashi, Takeshi; Pruski, Marek; Schurko, Robert W

    2016-06-29

    (14)N ultra-wideline (UW), (1)H{(15)N} indirectly-detected HETCOR (idHETCOR) and (15)N dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) experiments, in combination with plane-wave density functional theory (DFT) calculations of (14)N EFG tensors, were utilized to characterize a series of nitrogen-containing active pharmaceutical ingredients (APIs), including HCl salts of scopolamine, alprenolol, isoprenaline, acebutolol, dibucaine, nicardipine, and ranitidine. A case study applying these methods for the differentiation of polymorphs of bupivacaine HCl is also presented. All experiments were conducted upon samples with naturally-abundant nitrogen isotopes. For most of the APIs, it was possible to acquire frequency-stepped UW (14)N SSNMR spectra of stationary samples, which display powder patterns corresponding to pseudo-tetrahedral (i.e., RR'R''NH(+) and RR'NH2(+)) or other (i.e., RNH2 and RNO2) nitrogen environments. Directly-excited (14)N NMR spectra were acquired using the WURST-CPMG pulse sequence, which incorporates WURST (wideband, uniform rate, and smooth truncation) pulses and a CPMG (Carr-Purcell Meiboom-Gill) refocusing protocol. In certain cases, spectra were acquired using (1)H → (14)N broadband cross-polarization, via the BRAIN-CP (broadband adiabatic inversion - cross polarization) pulse sequence. These spectra provide (14)N electric field gradient (EFG) tensor parameters and orientations that are particularly sensitive to variations in local structure and intermolecular hydrogen-bonding interactions. The (1)H{(15)N} idHETCOR spectra, acquired under conditions of fast magic-angle spinning (MAS), used CP transfers to provide (1)H-(15)N chemical shift correlations for all nitrogen environments, except for two sites in acebutolol and nicardipine. One of these two sites (RR'NH2(+) in acebutolol) was successfully detected using the DNP-enhanced (15)N{(1)H} CP/MAS measurement, and one (RNO2 in nicardipine) remained elusive due to the absence of

  15. Synthesis of 15 alpha-hydroxyestrogen 15-N-acetylglucosaminides.

    PubMed

    Suzuki, E; Namba, S; Kurihara, H; Goto, J; Matsuki, Y; Nambara, T

    1995-03-01

    The synthesis of 15-N-acetylglucosaminides of 15 alpha-hydroxyesterone, 15 alpha-hydroxyestradiol, and 15 alpha-hydroxyestriol (estetrol) is described. The latter two were prepared by condensation of 2-acetamido-1 alpha-chloro-1,2-dideoxy-3,4,6-trio-O-acetyl-D-glucopyranose with appropriately protected 15 alpha-hydroxyestrogens by the Koenigs-Knorr reaction employing cadmium carbonate as a catalyst. Subsequent removal of protecting groups with methanolic potassium hydroxide provided the desired conjugates. 15 alpha-Hydroxyestrone 15-N-acetylglucosaminide was synthesized from the corresponding 15 alpha-hydroxyestradiol derivative by Jones oxidation followed by brief alkaline hydrolysis. These conjugates underwent enzymatic hydrolysis with beta-N-acetylglucosaminidase from Jack beans to produce 15 alpha-hydroxyestrogens. PMID:7792832

  16. Marking Drosophila suzukii (Diptera: Drosophilidae) With Rubidium or 15N.

    PubMed

    Klick, J; Yang, W Q; Bruck, D J

    2015-06-01

    Drosophila suzukii Matsumura (Diptera: Drosophilidae) has caused significant economic damage to berry and stone fruit production regions. Markers that are systemic in plants and easily transferred to target organisms are needed to track D. suzukii exploitation of host resources and trophic interactions. High and low concentrations of the trace element, rubidium (Rb), and the stable isotope, 15N, were tested to mark D. suzukii larvae feeding on fruits of enriched strawberry plants grown in containers under greenhouse conditions. Fly marker content and proportion of flies marked 1, 7, and 14 d after emergence from enriched fruits and fly dry mass were analyzed. Nearly 100% of the flies analyzed 14 d after emerging from 15N-enriched plants were marked, whereas only 30-75% and 0-3% were marked 14 d after emerging from high and low Rb concentration plants, respectively. Rapid Rb decay, strong 15N persistence, and the economics of using these markers in the field to elucidate D. suzukii pest ecology are discussed. PMID:26470275

  17. Nitrogen input 15N-signatures are reflected in plant 15N natural abundances of N-rich tropical forest in China

    NASA Astrophysics Data System (ADS)

    Abdisa Gurmesa, Geshere; Lu, Xiankai; Gundersen, Per; Yunting, Fang; Mo, Jiangming

    2016-04-01

    In this study, we tested the measurement of natural abundance of 15N15N) for its ability to assess changes in N cycling due to increased N deposition in two forest types; namely, an old-growth broadleaved forest and a pine forest, in southern China. We measured δ15N values of inorganic N in input and output fluxes under ambient N deposition, and N concentration and δ15N of major ecosystem compartments under ambient and increased N deposition. Our results showed that N deposition to the forests was 15N-depleted, and was dominated by NH4-N. Plants were 15N-depleted due to imprint from the 15N-depleted atmospheric N deposition. The old-growth forest had larger N concentration and was more 15N-enriched than the pine forest. Nitrogen addition did not significantly affect N concentration, but it significantly increased δ15N values of plants, and slightly more so in the pine forest, toward the 15N signature of the added N in both forests. The result indicates that the pine forest may rely more on the 15N-depleted deposition N. Soil δ15N values were slightly decreased by the N addition. Our result suggests that ecosystem δ15N is more sensitive to the changes in ecosystem N status and N cycling than N concentration in N-saturated sub-tropical forests.

  18. Sub-picosecond spin relaxation of bright excitons and imbalance suppression in asymmetric Cdse/Zns nanocrystal quantum dots under an applied magnetic field.

    PubMed

    Kyhm, Kwangseuk; Kim, Jihoon; Yang, Ho-Soon; Je, Koo-Chul; Murayama, Akihiro

    2012-03-01

    The ultrafast spin dynamics of the bright exciton in CdSe/ZnS nanocrystal quantum dots has been investigated using a circularly polarized pump-probe experiment. A remarkably fast spin flip (-500 fs) of the bright exciton was observed at 4 K, which is attributed to the anisotropic electron-hole exchange interaction and the random positioning of nanocrystal quantum dots. In the presence of an applied magnetic field (5 T), the exciton spin parallel to the external magnetic field was favored due to Zeeman splitting. We found that this imbalance can possibly be suppressed by the state-blocking and the mixing of the 1(L) and 1(U) states in asymmetric quantum dots.

  19. A spectral correlation function for efficient sequential NMR assignments of uniformly (15)N-labeled proteins.

    PubMed

    Bartels, C; Wüthrich, K

    1994-11-01

    A new computer-based approach is described for efficient sequence-specific assignment of uniformly (15)N-labeled proteins. For this purpose three-dimensional (15)N-correlated [(1)H, (1)H]-NOESY spectra are divided up into two-dimensional (1)H-(1)H strips which extend over the entire spectral width along one dimension and have a width of ca. 100 Hz, centered about the amide proton chemical shifts along the other dimension. A spectral correlation function enables sorting of these strips according to proximity of the corresponding residues in the amino acid sequence. Thereby, starting from a given strip in the spectrum, the probability of its corresponding to the C-terminal neighboring residue is calculated for all other strips from the similarity of their peak patterns with a pattern predicted for the sequentially adjoining residue, as manifested in the scalar product of the vectors representing the predicted and measured peak patterns. Tests with five different proteins containing both α-helices and β-sheets, and ranging in size from 58 to 165 amino acid residues show that the discrimination achieved between the sequentially neighboring residue and all other residues compares well with that obtained with an unguided interactive search of pairs of sequentially neighboring strips, with important savings in the time needed for complete analysis of 3D (15)N-correlated [(1)H, (1)H]-NOESY spectra. The integration of this routine into the program package XEASY ensures that remaining ambiguities can be resolved by visual inspection of the strips, combined with reference to the amino acid sequence and information on spin-system types obtained from additional NMR spectra.

  20. (1)H, (13)C and (15)N backbone resonance assignments and dynamic properties of the PDZ tandem of Whirlin.

    PubMed

    Delhommel, Florent; Wolff, Nicolas; Cordier, Florence

    2016-10-01

    Mammals perceive sounds thanks to mechanosensory hair cells located in the inner ear. The stereocilia of these cells are tightly bound together in bundles by a network of cadherins and scaffolding proteins. Stereocilia deflection induces stretching of this network and is responsible for hair cell depolarization that triggers the neuronal message, transducing the mechanical signal into an electric signal transmissible to the brain. Nearly all proteins involved in this mechano-electrical transduction network contain short C-terminal motifs of interaction with PDZ domains (PSD-95, Discs Large, ZO-1). Interestingly only two of these proteins encompass PDZ domains: Harmonin and Whirlin. As our first step towards a comprehensive structural study of Whirlin, we have assigned the (1)H, (13)C and (15)N backbone resonances of a tandem formed by the first two PDZ domains of Whirlin, reported the secondary structure elements of this tandem as predicted by the TALOS+ server and evaluated its dynamics from (15)N relaxation measurements.

  1. (1)H and (19)F spin-lattice relaxation and CH3 or CF3 reorientation in molecular solids containing both H and F atoms.

    PubMed

    Beckmann, Peter A; Rheingold, Arnold L

    2016-04-21

    The dynamics of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state (1)H and (19)F spin-lattice relaxationexperiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF3 reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance(NMR) time scale) to investigate CF3 reorientation occurring on the NMR time scale. The effects of (19)F-(19)F and (19)F-(1)H spin-spin dipolar interactions on the complicated nonexponential NMRrelaxation provide independent inputs into determining a model for CF3 reorientation. As such, these experiments provide much more information than when only one spin species (usually (1)H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH3 and CF3 reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components. PMID:27389221

  2. (1)H and (19)F spin-lattice relaxation and CH3 or CF3 reorientation in molecular solids containing both H and F atoms.

    PubMed

    Beckmann, Peter A; Rheingold, Arnold L

    2016-04-21

    The dynamics of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state (1)H and (19)F spin-lattice relaxationexperiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF3 reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance(NMR) time scale) to investigate CF3 reorientation occurring on the NMR time scale. The effects of (19)F-(19)F and (19)F-(1)H spin-spin dipolar interactions on the complicated nonexponential NMRrelaxation provide independent inputs into determining a model for CF3 reorientation. As such, these experiments provide much more information than when only one spin species (usually (1)H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH3 and CF3 reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components.

  3. Contribution of 19F resonances on 18O( p, α)15N reaction rate

    NASA Astrophysics Data System (ADS)

    Benmeslem, Meriem; Chafa, Azzedine; Barhoumi, Slimane; Tribeche, Mouloud

    2014-08-01

    The 18O( p, α)15N reaction influences the isotopes production such as 19F, 18O, and 15N which can be used to test the models of stellar evolution. 19F is synthesized in both asymptotic giant branch (AGB) and metal-rich Wolf-Rayet (WR) stars. Using R-matrix theory we allow new values of resonances parameters in 19F. We show that the most important contribution to the differential and total cross section at low energies, comes from the levels in 19F situated at resonances energies E R =151, 680 and 840 keV with spin and parity 1/2+. The total width of the 680 keV resonance is badly known. So, we have focused on this broad resonance corresponding to the 8.65 MeV level in 19F. We delimit the temperature range in which each resonance contribution to the total reaction rate occurs by analyzing the ratio ( N A < σν> i / N A < σν>). This allowed us to show that the 680 and 840 keV broad resonances strongly dominate the reaction rate over the stellar temperature range T 9=0.02-0.06 and T 9=0.5-5. Finally, these results were compared to NACRE and Iliadis astrophysical compilations.

  4. Incorporation of (15)N-TNT transformation products into humifying plant organic matter as revealed by one- and two-dimensional solid state NMR spectroscopy.

    PubMed

    Knicker, Heike

    2003-06-01

    Solid-state double cross polarization magic angle spinning (DCPMAS) 15N 13C nuclear magnetic resonance (NMR) spectroscopy was applied to study the incorporation of TNT transformation products into humifying plant organic matter. For this approach, 13C-enriched plant material (Lolium perenne) was mixed with quartz sand and aerobically incubated for 11 months after addition of 15N(3)-2,4,6-trinitrotoluene (TNT). After successive extraction of the incubate with water, methanol and ethyl acetate, approximately 60% of the 15N added as 15N(3)-TNT (15N(add)) remained in the solid organic residue (SOR-fraction). The acid insoluble fraction (AI) obtained after NaOH and HCl extractions contained approximately 20% of 15N(add). For both fractions, 15N NMR spectroscopy revealed an almost complete reduction of the TNT after 11 months of aerobic incubation. Most of the reduced nitrogen groups underwent further condensation. The corresponding DCPMAS NMR spectra allowed the identification of amides that are further substituted by alkyl groups that resist even acid hydrolysis. This assigns them to relatively stable compounds rather than to newly synthesized microbial peptides. The results of this study suggest further that the covalent binding of TNT transformation products to plant derived organic matter is mediated by alkylation and acetylation reactions, rather than by 1,4 addition of TNT-derived nitrogenous groups to quinones of the humic material.

  5. Selective observation of biologically important 15N-labeled metabolites in isolated rat brain and liver by 1H-detected multiple-quantum-coherence spectroscopy

    NASA Astrophysics Data System (ADS)

    Kanamori, Keiko; Ross, Brian D.; Parivar, Farhad

    Four cerebral metabolites of importance in neurotransmission, serotonin, L-tryptophan, L-glutamine, and N-acetyl- L-aspartate, and two hepatic urea-cycle intermediates, citrulline and urea, were found to be observable by 1H- 15N heteronuclear multiple-quantum-coherence (HMQC) spectroscopy in aqueous solution at physiological pH and temperature, through the protons spin-coupled to their indole, amide, or ureido nitrogen. Their 1H chemical shifts were well dispersed over a 5-10 ppm region while the 1J 15N- 1H values were 87-99 Hz. For [γ- 15N]glutamine, a 50- to 100-fold increase in sensitivity over direct 15N detection was achieved, in contrast to a 2-fold increase by the polarization-transfer method. In the isolated brain of portacaval-shunted rats, the amide protons of biologically 15N-enriched [γ- 15N]glutamine were observed in 2 min of acquisition, with suppression of proton signals from all other cerebral metabolites. In isolated liver of 15N-enriched control rats, [ 15NIurea protons were observed in 16 min. The HMQC method is likely to be effective for the in vivo study of cerebral and hepatic nitrogen metabolism.

  6. Modified Jeener Solid-Echo Pulse Sequences for the Measurement of the Proton Dipolar Spin-Lattice Relaxation-Time ( T1D) of Tissue Solid-like Macromolecular Components

    NASA Astrophysics Data System (ADS)

    Yang, H.; Schleich, T.

    Modified Jeener solid-echo pulse sequences are proposed for the measurement of the proton dipolar spin-lattice relaxation time, T1D, of motionally restricted (solid-like) components in the presence of mobile molecular species, such as encountered in biological tissue. A phase-cycled composite-pulse sequence was used for detection of the dipolar signal and cancellation of the Zeeman signal. A homospoil gradient pulse was added to the Jeener echo pulse sequence to enhance dephasing of the transverse magnetization components of mobile species, thereby aiding in elimination of the Zeeman signal during dipolar signal acquisition. A modified Jeener echo sequence incorporating water suppression is also proposed as a means to further depress the Zeeman signal arising from mobile components. The modified Jeener echo sequences were successfully used for the measurement of proton T1D values of solid 2,6-dimethylphenol and Sephadex gels of differing degrees of cross linking and hydration.

  7. General order parameter based correlation analysis of protein backbone motions between experimental NMR relaxation measurements and molecular dynamics simulations.

    PubMed

    Liu, Qing; Shi, Chaowei; Yu, Lu; Zhang, Longhua; Xiong, Ying; Tian, Changlin

    2015-02-13

    Internal backbone dynamic motions are essential for different protein functions and occur on a wide range of time scales, from femtoseconds to seconds. Molecular dynamic (MD) simulations and nuclear magnetic resonance (NMR) spin relaxation measurements are valuable tools to gain access to fast (nanosecond) internal motions. However, there exist few reports on correlation analysis between MD and NMR relaxation data. Here, backbone relaxation measurements of (15)N-labeled SH3 (Src homology 3) domain proteins in aqueous buffer were used to generate general order parameters (S(2)) using a model-free approach. Simultaneously, 80 ns MD simulations of SH3 domain proteins in a defined hydrated box at neutral pH were conducted and the general order parameters (S(2)) were derived from the MD trajectory. Correlation analysis using the Gromos force field indicated that S(2) values from NMR relaxation measurements and MD simulations were significantly different. MD simulations were performed on models with different charge states for three histidine residues, and with different water models, which were SPC (simple point charge) water model and SPC/E (extended simple point charge) water model. S(2) parameters from MD simulations with charges for all three histidines and with the SPC/E water model correlated well with S(2) calculated from the experimental NMR relaxation measurements, in a site-specific manner.

  8. Theory of nuclear magnetic relaxation

    NASA Technical Reports Server (NTRS)

    Mcconnell, J.

    1983-01-01

    A theory of nuclear magnetic interaction is based on the study of the stochastic rotation operator. The theory is applied explicitly to relaxation by anisotropic chemical shift and to spin-rotational interactions. It is applicable also to dipole-dipole and quadrupole interactions.

  9. Magnetism of the chromium thio-spinels Fe1-xCuxCr2S4 studied using muon spin rotation and relaxation.

    PubMed

    Kalvius, G M; Krimmel, A; Wäppling, R; Hartmann, O; Litterst, F J; Wagner, F E; Tsurkan, V; Loidl, A

    2013-05-01

    Powder samples of Fe1-xCuxCr2S4 with x = 0,0.2,0.5,0.8 were studied, between 5 and 300 K. The results reveal that for x < 1, the magnetic order in the series is more varied than the simple collinear ferrimagnetic structure traditionally assumed to exist everywhere from the Curie point to T → 0. In FeCr2S4 several ordered magnetic phases are present, with the ground state likely to have an incommensurate cone-like helical structure. Fe0.8Cu0.2Cr2S4 is the compound for which simple collinear ferrimagnetism is best developed. In Fe0.5Cu0.5Cr2S4 the ferrimagnetic spin structure is not stable, causing spin reorientation around 90 K. In Fe0.2Cu0.8Cr2S4 the ferrimagnetic structure is at low temperatures considerably distorted locally, but with rising temperature this disorder shows a rapid reduction, coupled to increased spin fluctuation rates. In summary, the present data show that the changes induced by the replacement of Fe by Cu have more profound influences on the magnetic properties of the Fe1-xCuxCr2S4 compounds than merely a shift of Curie temperature, saturation magnetization and internal field magnitude.

  10. Relaxation System

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Environ Corporation's relaxation system is built around a body lounge, a kind of super easy chair that incorporates sensory devices. Computer controlled enclosure provides filtered ionized air to create a feeling of invigoration, enhanced by mood changing aromas. Occupant is also surrounded by multidimensional audio and the lighting is programmed to change colors, patterns, and intensity periodically. These and other sensory stimulators are designed to provide an environment in which the learning process is stimulated, because research has proven that while an individual is in a deep state of relaxation, the mind is more receptive to new information.

  11. A general model to calculate the spin-lattice (T1) relaxation time of blood, accounting for haematocrit, oxygen saturation and magnetic field strength.

    PubMed

    Hales, Patrick W; Kirkham, Fenella J; Clark, Christopher A

    2016-02-01

    Many MRI techniques require prior knowledge of the T1-relaxation time of blood (T1bl). An assumed/fixed value is often used; however, T1bl is sensitive to magnetic field (B0), haematocrit (Hct), and oxygen saturation (Y). We aimed to combine data from previous in vitro measurements into a mathematical model, to estimate T1bl as a function of B0, Hct, and Y. The model was shown to predict T1bl from in vivo studies with a good accuracy (± 87 ms). This model allows for improved estimation of T1bl between 1.5-7.0 T while accounting for variations in Hct and Y, leading to improved accuracy of MRI-derived perfusion measurements.

  12. Triple resonance experiments for aligned sample solid-state NMR of 13C and 15N labeled proteins

    PubMed Central

    Sinha, Neeraj; Grant, Christopher V.; Park, Sang Ho; Brown, Jonathan Miles; Opella, Stanley J.

    2013-01-01

    Initial steps in the development of a suite of triple-resonance 1H/13C/15N solid-state NMR experiments applicable to aligned samples of 13C and 15N labeled proteins are described. The experiments take advantage of the opportunities for 13C detection without the need for homonuclear 13C/13C decoupling presented by samples with two different patterns of isotopic labeling. In one type of sample, the proteins are ~20% randomly labeled with 13C in all backbone and side chain carbon sites and ~100% uniformly 15N labeled in all nitrogen sites; in the second type of sample, the peptides and proteins are 13C labeled at only the α-carbon and 15N labeled at the amide nitrogen of a few residues. The requirement for homonuclear 13C/13C decoupling while detecting 13C signals is avoided in the first case because of the low probability of any two 13C nuclei being bonded to each other; in the second case, the labeled 13Cα sites are separated by at least three bonds in the polypeptide chain. The experiments enable the measurement of the 13C chemical shift and 1H–13C and 15N–13C heteronuclear dipolar coupling frequencies associated with the 13Cα and 13C′ backbone sites, which provide orientation constraints complementary to those derived from the 15N labeled amide backbone sites. 13C/13C spin-exchange experiments identify proximate carbon sites. The ability to measure 13C–15N dipolar coupling frequencies and correlate 13C and 15N resonances provides a mechanism for making backbone resonance assignments. Three-dimensional combinations of these experiments ensure that the resolution, assignment, and measurement of orientationally dependent frequencies can be extended to larger proteins. Moreover, measurements of the 13C chemical shift and 1H–13C heteronuclear dipolar coupling frequencies for nearly all side chain sites enable the complete three-dimensional structures of proteins to be determined with this approach. PMID:17293139

  13. Simultaneous cross polarization to 13C and 15N with 1H detection at 60 kHz MAS solid-state NMR

    NASA Astrophysics Data System (ADS)

    Das, Bibhuti B.; Opella, Stanley J.

    2016-01-01

    We describe high resolution MAS solid-state NMR experiments that utilize 1H detection with 60 kHz magic angle spinning; simultaneous cross-polarization from 1H to 15N and 13C nuclei; bidirectional cross-polarization between 13C and 15N nuclei; detection of both amide nitrogen and aliphatic carbon 1H; and measurement of both 13C and 15N chemical shifts through multi-dimensional correlation experiments. Three-dimensional experiments correlate amide 1H and alpha 1H selectively with 13C or 15N nuclei in a polypeptide chain. Two separate three-dimensional spectra correlating 1Hα/13Cα/1HN and 1HN/15N/1Hα are recorded simultaneously in a single experiment, demonstrating that a twofold savings in experimental time is potentially achievable. Spectral editing using bidirectional coherence transfer pathways enables simultaneous magnetization transfers between 15N, 13Cα(i) and 13C‧(i-1), facilitating intra- and inter-residue correlations for sequential resonance assignment. Non-uniform sampling is integrated into the experiments, further reducing the length of experimental time.

  14. Ballistic spin resonance.

    PubMed

    Frolov, S M; Lüscher, S; Yu, W; Ren, Y; Folk, J A; Wegscheider, W

    2009-04-16

    The phenomenon of spin resonance has had far-reaching influence since its discovery 70 years ago. Electron spin resonance driven by high-frequency magnetic fields has enhanced our understanding of quantum mechanics, and finds application in fields as diverse as medicine and quantum information. Spin resonance can also be induced by high-frequency electric fields in materials with a spin-orbit interaction; the oscillation of the electrons creates a momentum-dependent effective magnetic field acting on the electron spin. Here we report electron spin resonance due to a spin-orbit interaction that does not require external driving fields. The effect, which we term ballistic spin resonance, is driven by the free motion of electrons that bounce at frequencies of tens of gigahertz in micrometre-scale channels of a two-dimensional electron gas. This is a frequency range that is experimentally challenging to access in spin resonance, and especially difficult on a chip. The resonance is manifest in electrical measurements of pure spin currents-we see a strong suppression of spin relaxation length when the oscillating spin-orbit field is in resonance with spin precession in a static magnetic field. These findings illustrate how the spin-orbit interaction can be harnessed for spin manipulation in a spintronic circuit, and point the way to gate-tunable coherent spin rotations in ballistic nanostructures without external alternating current fields. PMID:19370029

  15. Relaxation times estimation in MRI

    NASA Astrophysics Data System (ADS)

    Baselice, Fabio; Caivano, Rocchina; Cammarota, Aldo; Ferraioli, Giampaolo; Pascazio, Vito

    2014-03-01

    Magnetic Resonance Imaging is a very powerful techniques for soft tissue diagnosis. At the present, the clinical evaluation is mainly conducted exploiting the amplitude of the recorded MR image which, in some specific cases, is modified by using contrast enhancements. Nevertheless, spin-lattice (T1) and spin-spin (T2) relaxation times can play an important role in many pathology diagnosis, such as cancer, Alzheimer or Parkinson diseases. Different algorithms for relaxation time estimation have been proposed in literature. In particular, the two most adopted approaches are based on Least Squares (LS) and on Maximum Likelihood (ML) techniques. As the amplitude noise is not zero mean, the first one produces a biased estimator, while the ML is unbiased but at the cost of high computational effort. Recently the attention has been focused on the estimation in the complex, instead of the amplitude, domain. The advantage of working with real and imaginary decomposition of the available data is mainly the possibility of achieving higher quality estimations. Moreover, the zero mean complex noise makes the Least Square estimation unbiased, achieving low computational times. First results of complex domain relaxation times estimation on real datasets are presented. In particular, a patient with an occipital lesion has been imaged on a 3.0T scanner. Globally, the evaluation of relaxation times allow us to establish a more precise topography of biologically active foci, also with respect to contrast enhanced images.

  16. Heteronuclear Cross-Relaxation Effects in the NMR Spectroscopy of Hyperpolarized Targets

    PubMed Central

    Donovan, Kevin J.; Lupulescu, Adonis; Frydman, Lucio

    2016-01-01

    Dissolution DNP enables high-sensitivity solution phase NMR experiments on long-lived nuclear spin species such as 15N and 13C. This report explores certain features arising in solution-state 1H NMR, upon polarizing low-γ nuclear species. Following solid state hyperpolarization of both 13C and 1H, solution-phase 1H NMR experiments on dissolved samples revealed transient effects whereby peaks arising from protons bonded to the naturally-occurring 13C nuclei, appeared larger than the typically dominant 12C-bonded 1H resonances. This enhancement of the satellite-peaks was examined in detail, with respect to a variety of mechanisms that could potentially originate it. Both two- and three-spin phenomena active in the solid state could lead to this kind of effect; still, experimental observations revealed that the enhancement originates from 13C→1H polarization transfer processes active in the liquid state. Kinetic equations based on modified heteronuclear cross-relaxation models were examined, and found to describe well the distinct patterns of growth and decay shown by the 13C-bound 1H NMR satellite resonances. The dynamics of these novel cross-relaxation phenomena were determined, and their potential usefulness as tools for investigating hyperpolarized ensembles and for obtaining enhanced-sensitivity 1H NMR traces, is explored. PMID:24403222

  17. Temperature-dependent 11B spin-lattice relaxation time for BF4 and CF3BF3 anions in room-temperature ionic liquids.

    PubMed

    Hayamizu, Kikuko; Tsuzuki, Seiji; Seki, Shiro

    2011-01-01

    Temperature-dependent (11)B T(1) values were measured for the BF(4) anion and BF(3) in the CF(3)BF(3) anion in room-temperature ionic liquids (RTILs) composed of the cation N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME). Including the lithium-salt-doped samples, two neat and two binary ionic liquids were studied. Arrhenius plots of the (11)B T(1) showed T(1) minima for BF(4) in the temperature range between 243 (or above freezing) and 373 K. Using the Bloembergen, Pound, and Purcell(BPP) equations for the (11)B quadrupolar and (11)B-(19) F dipolar relaxation mechanisms, the correlation times for motions of BF(4) were calculated. Since the internal rotation of BF(3) is assumed in CF(3)BF(3), T(1) minimum was not observed. The effects of the addition of the lithium salt on the (11)B correlation time and (11)BT(1) for the anions in the ILs are discussed. PMID:21162135

  18. Spin transport in nanoscale spin valves and magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Patibandla, Sridhar

    Spintronics or electronics that utilizes the spin degree of freedom of a single charge carrier (or an ensemble of charge carriers) to store, process, sense or communicate data and information is a rapidly burgeoning field in electronics. In spintronic devices, information is encoded in the spin polarization of a single carrier (or multiple carriers) and the spin(s) of these carrier(s) are manipulated for device operation. This strategy could lead to devices with low power consumption. This dissertation investigates spin transport in one dimensional and two dimensional semiconductors, with a view to applications in spintronic devices. This dissertation is arranged as follows: Chapter 1 gives a detailed introduction and necessary background to understand aspects of spin injection into a semiconductor from a spin polarized source such as a ferromagnet, and spin polarized electron transport in the semiconductor. Chapter 2 discusses the nanoporous alumina technique that is employed to fabricate nanowires and nanowire spin valves for the investigation of spin transport in 1D semiconductors. Chapter 3 investigates the spin transport in quasi one-dimensional spin valves with germanium spacer layer. These spin valves with 50nm in diameter and 1 mum length were fabricated using the porous alumina technique. Spin transport in nanoscale germanium spin valves was demonstrated and the spin relaxation lengths and the spin relaxation times were calculated. Chapter 4 discusses spin transport studies conducted in bulk high purity germanium with a view to comparing spin relaxation mechanisms in low mobility nanowires and high mobility bulk structures. Lateral spin valve with tunnel injectors were employed in this study and the spin transport measurements were conducted at various temperatures. The spin relaxation rates were measured as a function of temperature which allowed us to distinguish between two different mechanisms---D'yakonov-Perel' and Elliott-Yafet---that dominate spin

  19. Hyperpolarized 13C urea relaxation mechanism reveals renal changes in diabetic nephropathy

    PubMed Central

    Stokholm Nørlinger, Thomas; Christoffer Hansen, David; Qi, Haiyun; Mose Nielsen, Per; Bonde Bertelsen, Lotte; Henrik Ardenkjaer‐Larsen, Jan; Stødkilde Jørgensen, Hans

    2015-01-01

    Purpose Our aim was to assess a novel 13C radial fast spin echo golden ratio single shot method for interrogating early renal changes in the diabetic kidney, using hyperpolarized (HP) [13C,15N2]urea as a T2 relaxation based contrast bio‐probe. Methods A novel HP 13C MR contrast experiment was conducted in a group of streptozotocin type‐1 diabetic rat model and age matched controls. Results A significantly different relaxation time (P = 0.004) was found in the diabetic kidney (0.49 ± 0.03 s) compared with the controls (0.64 ± 0.02 s) and secondly, a strong correlation between the blood oxygen saturation level and the relaxation times were observed in the healthy controls. Conclusion HP [13C,15N2]urea apparent T2 mapping may be a useful for interrogating local renal pO2 status and renal tissue alterations. Magn Reson Med, 2015. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. Magn Reson Med 75:515–518, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. PMID:26584247

  20. Measurement of Spin-Lattice Relaxation Times and Concentrations in Systems with Chemical Exchange Using the One-Pulse Sequence: Breakdown of the Ernst Model for Partial Saturation in Nuclear Magnetic Resonance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Spencer, Richard G. S.; Fishbein, Kenneth W.

    2000-01-01

    A fundamental problem in Fourier transform NMR spectroscopy is the calculation of observed resonance amplitudes for a repetitively pulsed sample, as first analyzed by Ernst and Anderson in 1966. Applications include determination of spin-lattice relaxation times (T1's) by progressive saturation and correction for partial saturation in order to determine the concentrations of the chemical constituents of a spectrum. Accordingly, the Ernst and Anderson formalism has been used in innumerable studies of chemical and, more recently, physiological systems. However, that formalism implicitly assumes that no chemical exchange occurs. Here, we present an analysis of N sites in an arbitrary chemical exchange network, explicitly focusing on the intermediate exchange rate regime in which the spin-lattice relaxation rates and the chemical exchange rates are comparable in magnitude. As a special case of particular importance, detailed results are provided for a system with three sites undergoing mutual exchange. Specific properties of the N-site network are then detailed. We find that (i) the Ernst and Anderson analysis describing the response of a system to repetitive pulsing is inapplicable to systems with chemical exchange and can result in large errors in T1 and concentration measurements; (ii) T1's for systems with arbitrary exchange networks may still be correctly determined from a one-pulse experiment using the Ernst formula, provided that a short interpulse delay time and a large flip angle are used; (iii) chemical concentrations for exchanging systems may be correctly determined from a one-pulse experiment either by using a short interpulse delay time with a large flip angle, as for measuring T1's, and correcting for partial saturation by use of the Ernst formula, or directly by using a long interpulse delay time to avoid saturation; (iv) there is a significant signal-to-noise penalty for performing one-pulse experiments under conditions which permit accurate

  1. Measuring denitrification after grassland renewal and grassland conversion to cropland by using the 15N gas-flux method

    NASA Astrophysics Data System (ADS)

    Buchen, Caroline; Eschenbach, Wolfram; Flessa, Heinz; Giesemann, Anette; Lewicka-Szczebak, Dominika; Well, Reinhard

    2015-04-01

    Denitrification, the reduction of oxidized forms of inorganic N to N2O and N2 is an important pathway of gaseous nitrogen losses. Measuring denitrification, especially the reduction of N2O to N2, expressed in the product ratio (N2O/(N2O + N2)), is rather difficult and hence rarely performed under field conditions. But using the 15N gas-flux method allows determining N transformation processes in their natural environment. In order to develop effective climate mitigation strategies understanding the N2O source is essential. We used the 15N gas-flux method to determine N2O and N2 emissions following grassland renewal and conversion techniques. Therefore we selected three different treatments: control (C), mechanical grassland renovation (GR) (autumn 2013) and grassland conversion to maize (GM) (spring 2014) from field plot trials on two different sites (Histic Gleysoil and Plaggic Anthrosol) near Oldenburg, Lower Saxony, Germany. We applied 15N labeled KNO3- (60 atom. % 15N) at a rate equivalent to common farming practices (150 kg N*ha-1) using needle injection of fertilizer solution in three different depths (10 cm, 15 cm, 20 cm) for homogeneous soil labeling up to 30 cm in microplots. During the first 10 days after application (May 2014) gas flux measurements from closed chambers were performed every second day and then weekly following a period of 8 weeks. Gas samples were analyzed for δ15N of N2 and N2O by IRMS according to Lewicka-Szczebak et al. (2013). Concentration and 15N enrichment of NO3- in soil water was determined on weekly samples using the SPIN-MAS technique (Stange et al. 2007). Fluxes of N2 and N2O evolved from the 15N labeled soil nitrogen pool were calculated using the equations of Spott et al. (2006). Peak events of N2 and N2O emissions occurred during the first 10 days of measurement, showing differences in soil types, as well as treatment variations. N2 fluxes up to 178 g*ha-1*day-1 and N2O fluxes up to 280 g*ha-1*day-1 were measured on the

  2. Emergent spin electromagnetism induced by magnetization textures in the presence of spin-orbit interaction (invited)

    SciTech Connect

    Tatara, Gen; Nakabayashi, Noriyuki

    2014-05-07

    Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.

  3. 15N2 formation and fast oxygen isotope exchange during pulsed 15N18O exposure of MnOx/CeO2

    SciTech Connect

    Kwak, Ja Hun; Szanyi, Janos

    2014-12-23

    Pulsing 15N18O onto an annealed 1% Mn16Ox/Ce16O2 catalyst resulted in very fast oxygen isotope exchange and 15N2 formation at 295 K. In the 1st 15N18O pulse, due to the presence of large number of surface oxygen defects, extensive 15N218O and 15N2 formations were observed. In subsequent pulses oxygen isotope exchange dominated as a result of highly labile oxygen in the oxide. We gratefully acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy/Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

  4. Molecular determinants for drug-receptor interactions. 8. Anisotropic and internal motions in morphine, nalorphine, oxymorphone, naloxone and naltrexone in aqueous solution by carbon-13 NMR spin-lattice relaxation times

    NASA Astrophysics Data System (ADS)

    Grassi, Antonio; Perly, Bruno; Pappalardo, Giuseppe C.

    1989-02-01

    Carbon-13 NMR spin-lattice relaxation times ( T1) were measured for morphine, oxymorphone, nalorphine, naloxone and naltrexone as hydrochloride salts in 2H 2O solution. The data refer to the molecules in the N-equatorial configuration. The experimental T1 values were interpreted using a model of anisotropic reorientation of a rigid body with superimposed internal motions of the flexible N-methyl, N-methyl-allyl and N-methyl-cyclopropyl fragments. The calculated internal motional rates were found to markedly decrease on passing from agonists to mixed (nalorphine) and pure (naloxone, naltrexone) antagonists. For these latter the observed trend of the internal flexibility about NC and CC bonds of the N-substituents is discussed in terms of a correlation with their relative antagonistic potencies. In fact, such an evidence of decreasing internal conformational dynamics in the order nalorphine, naloxone, naltrexone, appeared interestingly in line with the "two-state" model of opiate receptor operation mode proposed by Snyder.

  5. Time-efficient determination of spin compartments by time-encoded pCASL T2-relaxation-under-spin-tagging and its application in hemodynamic characterization of the cerebral border zones.

    PubMed

    Schmid, Sophie; Teeuwisse, Wouter M; Lu, Hanzhang; van Osch, Matthias J P

    2015-12-01

    Information on water-transport across the blood-brain barrier can be determined from the T2 of the arterial spin labeling (ASL) signal. However, the current approach of using separate acquisitions of multiple inversion times is too time-consuming for clinical (research) applications. The aim of this study was to improve the time-efficiency of this method by combining it with time-encoded pseudo-continuous ASL (te-pCASL). Furthermore, the hemodynamic properties of the border zone regions in the brains of healthy, young volunteers were characterized as an example application. The use of te-pCASL instead of multi-TI pCASL significantly reduced the total scan duration, while providing a higher temporal resolution. A significantly lower cerebral blood flow (CBF) was found in the border zone regions compared with the central regions in both the posterior and the middle cerebral artery (MCA) flow territory. The arterial transit time (ATT) was almost two times longer in the border zone regions than in the central regions (p<0.05), with an average delay in ATT of 382ms in the posterior and 539ms in the MCA flow territory. When corrected for the ATT, the change in T2 over time was not significantly different for the border zones as compared to the central regions. In conclusion, te-pCASL-TRUST provided a time-efficient method to distinguish spin compartments based on their T2. The ATT in the border zone is significantly longer than in the central region. However, the exchange of the label from the arterial to the tissue compartment appears to be at a similar rate.

  6. Nuclear magnetic resonance study of the Schiff base in bacteriorhodopsin: Counterion effects on the sup 15 N shift anisotropy

    SciTech Connect

    de Groot, H.J.M.; Harbison, G.S.; Herzfeld, J.; Griffin, R.G. )

    1989-04-18

    High-resolution, solid-state {sup 15}N NMR has been used to study the chemical shift anisotropies of the Schiff bases in bacteriorhodopsin (bR) and in an extensive series of model compounds. Using slow-spinning techniques, the authors are able to obtain sufficient rotational sideband intensity to determine the full {sup 15}N chemical shift anisotropy for the Schiff base nitrogen in bR{sub 548} and bR{sub 568}. Comparisons are made between all-trans-bR{sub 568} and N-all-trans-retinylidene butylimine salts with halide, phenolate, and carboxylate counterions. It is argues that for the model compounds the variation in {sup 15}N chemical shift reflects the variation in (hydrogen) bond strength with the various counterions. The results suggest that carboxylates and tyrosinates may form hydrogen bonds of comparable strength in a hydrophobic environment. Thus, the hydrogen bonding strength of a counterion depends on factors that are not completely reflected in the solution pK{sub a} of its conujugate acid. For the model compounds, the two most downfield principal values of the {sup 15}N chemical shift tensor, {sigma}{sub 22} and {sigma}{sub 33}, vary dramatically with different counterions, whereas {sigma}{sub 11} remains essentially unaffected. In addition, there exists a linear correlation between {sigma}{sub 22} and {sigma}{sub 33}, which suggests that a single mechanism is responsible for the variation in chemical shifts present in all three classes of model compounds. The data for bR{sub 568} follow this trend, but the isotropic shift is 11 ppm further upfield than any of the model compounds. This extreme value suggests an unusually weak hydrogen bond in the protein.

  7. Synthesis of 13C and 15N labeled 2,4-dinitroanisole.

    PubMed

    Jagadish, Bhumasamudram; Field, Jim A; Chorover, Jon; Sierra-Alvarez, Reyes; Abrell, Leif; Mash, Eugene A

    2014-05-30

    Syntheses of [(13)C6]-2,4-dinitroanisole (ring-(13)C6) from [(13)C6]-anisole (ring-(13)C6) and [(15)N2]-2,4-dinitroanisole from anisole using in situ generated acetyl nitrate and [(15)N]-acetyl nitrate, respectively, are described. Treatment of [(13)C6]-anisole (ring-(13)C6) with acetyl nitrate generated in 100% HNO3 gave [(13)C6]-2,4-dinitroanisole (ring-(13)C6) in 83% yield. Treatment of anisole with [(15)N]-acetyl nitrate generated in 10 N [(15)N]-HNO3 gave [(15)N2 ]-2,4-dinitroanisole in 44% yield after two cycles of nitration. Byproducts in the latter reaction included [(15)N]-2-nitroanisole and [(15)N]-4-nitroanisole.

  8. The “Speedy” Synthesis of Atom-Specific 15N Imino/Amido-Labeled RNA

    PubMed Central

    Kreutz, Christoph; Micura, Ronald

    2016-01-01

    Although numerous reports on the synthesis of atom-specific 15N-labeled nucleosides exist, fast and facile access to the corresponding phosphoramidites for RNA solid-phase synthesis is still lacking. This situation represents a severe bottleneck for NMR spectroscopic investigations on functional RNAs. Here, we present optimized procedures to speed up the synthesis of 15N(1) adenosine and 15N(1) guanosine amidites, which are the much needed counterparts of the more straightforward-to-achieve 15N(3) uridine and 15N(3) cytidine amidites in order to tap full potential of 1H/15N/15N-COSY experiments for directly monitoring individual Watson–Crick base pairs in RNA. Demonstrated for two preQ1 riboswitch systems, we exemplify a versatile concept for individual base-pair labeling in the analysis of conformationally flexible RNAs when competing structures and conformational dynamics are encountered. PMID:26237536

  9. Relaxation Mechanisms in Hyperpolarized Polycrystalline ^129Xe

    NASA Astrophysics Data System (ADS)

    Samuelson, G.; Su, T.; Saam, B.

    2002-10-01

    Through spin exchange with optically polarized Rb vapor, it is possible to achieve upwards of 30% nuclear spin polarization in ^129Xe and a corresponding NMR signal some 5 orders of magnitude stronger than typical thermally polarized ^129Xe. Due to such a strong signal, hyperpolarized ^129Xe is being used for several leading-edge technologies (eg. biochemical spectroscopy, MRI, and polarization transfer). We have measured the nuclear spin relaxation rate of polycrystalline hyperpolarized ^129Xe at 77K (well below the freezing point of 160K) in a magnetic field of only a few Gauss and have observed that the hyperpolarization completely survives the freezing process. Furthermore, in this regime we have observed non-exponential spin relaxation that depends strongly on magnetic field, isotopic concentration (between ^129Xe and ^131Xe) and differences in crystallite formation. We present a simple spin-diffusion model that fits and explains the features of the data. Our results agree with the hypothesis that at low fields and temperatures the dominant spin relaxation mechanism is cross-relaxation with ^131Xe on the surface of the crystallites (Gatzke, et al., PRL b70, 690 (1993)).

  10. 15N solid-state nuclear magnetic resonance study of pyrolyzed metal-polyaniline cathode catalysts for oxygen reduction in fuel cells

    NASA Astrophysics Data System (ADS)

    Kuroki, Shigeki; Hosaka, Yo; Yamauchi, Chiharu; Nagata, Shinsuke; Sonoda, Mayu

    2015-09-01

    The oxygen reduction reaction (ORR) activity of pyrolyzed metal-free and metal (Mn, Fe, Co, Ni and Cu)-containing polyaniline (PANI) in polymer electrolyte fuel cell (PEFC) was studied. The metal-free PANI800 shows quite poor ORR catalytic activity, whilst the metal-containing PANIMe800 display a better ORR activity. The 15N CP/MAS NMR spectra of PANINi800 and PANICu800 show one weak peak at 118 ppm and there is no peak observed in PANIFe800, against that of PANI800, PANIMn800, PANICo800 and PANINi800 show two peaks at 273 and 118 ppm assigned to the pyridinic and pyridinium nitrogens. It is because of the paramagnetic effect of metal ions. The 15N spin-echo NMR spectra of PANIMe800 with fast recycle delay show the peaks at 140 and 270 ppm assigned to the graphitic and pyridinic nitrogens, against that of PANI800 shows no peak. The spectra of PANIMn800, PANICo800, PANINi800 and PANICu600 also contain a very broaden peak at 430 ppm assigned to the nitrogen with Fermi-contact effect from metal ions. The spectra of PANIFe800 show some spinning side bands and the average Fe3+-15N distance can be calculated. The some amount of iron ion are relieved and average Fe3+-15N distance increase after acid washing and the ORR activity decreases.

  11. Numerical evaluation of subsoil diffusion of (15) N labelled denitrification products during employment of the (15) N gas flux method in the field

    NASA Astrophysics Data System (ADS)

    Well, Reinhard; Buchen, Caroline; Lewicka-Szczebak, Dominika; Ruoss, Nicolas

    2016-04-01

    Common methods for measuring soil denitrification in situ include monitoring the accumulation of 15N labelled N2 and N2O evolved from 15N labelled soil nitrate pool in soil surface chambers. Gas diffusion is considered to be the main accumulation process. Because accumulation of the gases decreases concentration gradients between soil and chamber over time, gas production rates are underestimated if calculated from chamber concentrations. Moreover, concentration gradients to the non-labelled subsoil exist, inevitably causing downward diffusion of 15N labelled denitrification products. A numerical model for simulating gas diffusion in soil was used in order to determine the significance of this source of error. Results show that subsoil diffusion of 15N labelled N2 and N2O - and thus potential underestimation of denitrification derived from chamber fluxes - increases with cover closure time as well as with increasing diffusivity. Simulations based on the range of typical gas diffusivities of unsaturated soils show that the fraction of subsoil diffusion after chamber closure for 1 hour is always significant with values up to >30 % of total production of 15N labelled N2 and N2O. Field experiments for measuring denitrification with the 15N gas flux method were conducted. The ability of the model to predict the time pattern of gas accumulation was evaluated by comparing measured 15N2 concentrations and simulated values.

  12. Sensitivity-Enhanced MQ-HCN-CCH-TOCSY and MQ-HCN-CCH-COSY Pulse Schemes for 13C/ 15N Labeled RNA Oligonucleotides

    NASA Astrophysics Data System (ADS)

    Hu, Weidong; Jiang, Licong; Gosser, Yuying Q.

    2000-07-01

    Sensitivity enhanced multiple-quantum 3D HCN-CCH-TOCSY and HCN-CCH-COSY experiments are presented for the ribose resonance assignment of 13C/15N-labeled RNA sample. The experiments make use of the chemical shift dispersion of N1/N9 of pyrimidine/purine to distinguish the ribose spin systems. They provide a complementary approach for the assignment of ribose resonance to the currently used HCCH-COSY and HCCH-TOCSY type experiments in which either 13C or 1H is utilized to separate the different ribose spin systems. The pulse schemes have been demonstrated on a 23-mer 13C/15N-labeled RNA aptamer complexed with neomycin and tested on a 32-mer RNA complexed with a 23-residue peptide.

  13. General order parameter based correlation analysis of protein backbone motions between experimental NMR relaxation measurements and molecular dynamics simulations

    SciTech Connect

    Liu, Qing; Shi, Chaowei; Yu, Lu; Zhang, Longhua; Xiong, Ying; Tian, Changlin

    2015-02-13

    Internal backbone dynamic motions are essential for different protein functions and occur on a wide range of time scales, from femtoseconds to seconds. Molecular dynamic (MD) simulations and nuclear magnetic resonance (NMR) spin relaxation measurements are valuable tools to gain access to fast (nanosecond) internal motions. However, there exist few reports on correlation analysis between MD and NMR relaxation data. Here, backbone relaxation measurements of {sup 15}N-labeled SH3 (Src homology 3) domain proteins in aqueous buffer were used to generate general order parameters (S{sup 2}) using a model-free approach. Simultaneously, 80 ns MD simulations of SH3 domain proteins in a defined hydrated box at neutral pH were conducted and the general order parameters (S{sup 2}) were derived from the MD trajectory. Correlation analysis using the Gromos force field indicated that S{sup 2} values from NMR relaxation measurements and MD simulations were significantly different. MD simulations were performed on models with different charge states for three histidine residues, and with different water models, which were SPC (simple point charge) water model and SPC/E (extended simple point charge) water model. S{sup 2} parameters from MD simulations with charges for all three histidines and with the SPC/E water model correlated well with S{sup 2} calculated from the experimental NMR relaxation measurements, in a site-specific manner. - Highlights: • Correlation analysis between NMR relaxation measurements and MD simulations. • General order parameter (S{sup 2}) as common reference between the two methods. • Different protein dynamics with different Histidine charge states in neutral pH. • Different protein dynamics with different water models.

  14. Regulation of [15N]urea synthesis from [5-15N]glutamine. Role of pH, hormones, and pyruvate.

    PubMed

    Nissim, I; Yudkoff, M; Brosnan, J T

    1996-12-01

    We have utilized both [5-15N]glutamine and [3-13C] pyruvate as metabolic tracers in order to: (i) examine the effect of pH, glucagon (GLU), or insulin on the precursor-product relationship between 15NH3, [15N]citrulline, and, thereby, [15N]urea synthesis and (ii) elucidate the mechanism(s) by which pyruvate stimulates [15N] urea synthesis. Hepatocytes isolated from rat were incubated at pH 6.8, 7.4, or 7.6 with 1 mM [5-15N]glutamine and 0.1 mM 14NH4Cl in the presence or the absence of [3-13C] pyruvate (2 mM). A separate series of experiments was performed at pH 7.4 in the presence of insulin or GLU. 15NH3 enrichment exceeded or was equal to that of [15N]citrulline under all conditions except for pH 7.6, when the 15N enrichment in citrulline exceeded that in ammonia. The formation of [15N]citrulline (atom % excess) was increased with higher pH. Flux through phosphate-dependent glutaminase (PDG) and [15N]urea synthesis were stimulated (p < 0.05) at pH 7.6 or with GLU and decreased (p < 0.05) at pH 6.8. Insulin had no significant effect on flux through PDG or on [15N]urea synthesis. Decreased [15N]urea production at pH 6.8 was associated with depleted aspartate and glutamate levels. Pyruvate attenuated this decrease in the aspartate and glutamate pools and stimulated [15N]urea synthesis. Production of Asp from pyruvate was increased with increasing medium pH. Approximately 80% of Asp was derived from [3-13C]pyruvate regardless of incubation pH or addition of hormone. Furthermore, approximately 20, 40, and 50% of the mitochondrial N-acetylglutamate (NAG) pool was derived from [3-13C]pyruvate at pH 6.8, 7.4, and 7.6, respectively. Both the concentration and formation of [13C]NAG from [3-13C]pyruvate were increased (p < 0.05) with glucagon and decreased (p < 0.05) with insulin or at pH 6.8. The data suggest a correlation between changes in [15N]urea synthesis and alterations in the level and synthesis of [13C]NAG from pyruvate. The current observations suggest that the

  15. Spin-locking and cross-polarization under magic-angle spinning of uniformly labeled solids.

    PubMed

    Hung, Ivan; Gan, Zhehong

    2015-07-01

    Spin-locking and cross-polarization under magic-angle spinning are investigated for uniformly (13)C and (15)N labeled solids. In particular, the interferences from chemical shift anisotropy, and (1)H heteronuclear and (13)C homonuclear dipolar couplings are identified. The physical origin of these interferences provides guidelines for selecting the best (13)C and (15)N polarization transfer rf fields. Optimal settings for both the zero- and double-quantum cross-polarization transfer mechanisms are recommended.

  16. Ballistic spin resonance in multisubband quantum wires

    NASA Astrophysics Data System (ADS)

    Hachiya, Marco O.; Usaj, Gonzalo; Egues, J. Carlos

    2014-03-01

    Ballistic spin resonance was experimentally observed in a quasi-one-dimensional wire by Frolov et al. [Nature (London) 458, 868 (2009), 10.1038/nature07873]. The spin resonance was generated by a combination of an external static magnetic field and the oscillating effective spin-orbit magnetic field due to periodic bouncings of the electrons off the boundaries of a narrow channel. An increase of the D'yakonov-Perel spin relaxation rate was observed when the frequency of the spin-orbit field matched that of the Larmor precession frequency around the external magnetic field. Here we develop a model to account for the D'yakonov-Perel mechanism in multisubband quantum wires with both the Rashba and Dresselhaus spin-orbit interactions. Considering elastic spin-conserving impurity scatterings in the time-evolution operator (Heisenberg representation), we extract the spin relaxation time by evaluating the time-dependent expectation value of the spin operators. The magnetic field dependence of the nonlocal voltage, which is related to the spin relaxation time behavior, shows a wide plateau, in agreement with the experimental observation. This plateau arises due to injection in higher subbands and small-angle scattering. In this quantum mechanical approach, the spin resonance occurs near the spin-orbit-induced energy anticrossings of the quantum wire subbands with opposite spins. We also predict anomalous dips in the spin relaxation time as a function of the magnetic field in systems with strong spin-orbit couplings.

  17. Phase transitions in semidefinite relaxations

    PubMed Central

    Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico

    2016-01-01

    Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern dat